\documentclass{article}

\usepackage{xltxtra,fontspec}
\setmainfont[Mapping=tex-text]{DejaVu Serif}
\setmonofont[Scale=0.95]{DejaVu Sans Mono}
\newfontfamily\verbfont[Scale=0.8]{DejaVu Sans Mono}
\newfontfamily\ar[Script=Arabic]{DejaVu Sans}
\newfontfamily\ja{VL Gothic}
\newfontfamily\javerbfont[Scale=0.85,LetterSpace=5.0]{VL Gothic}

\usepackage{tikz}
\usepackage{tikz-qtree}

\usepackage{fullpage}

\usepackage{fancyvrb,fvrb-ex}
\fvset{gobble=0,xleftmargin=0.5in,xrightmargin=2.75in,formatcom=\verbfont}
\VerbatimFootnotes

\newcommand\tikztree{\texttt{tikz-qtree}}

\tikzset{>=latex}

\title{\tikztree: better trees with TikZ}
\author{David Chiang}
\date{Version 1.1 (Christmas 2009)}

\begin{document}

\maketitle

The \tikztree{} package provides a macro for drawing trees with
TikZ\footnote{\texttt{http://sourceforge.net/projects/pgf/}} using the
easy syntax of Alexis Dimitriadis'
Qtree\footnote{\texttt{http://www.ling.upenn.edu/advice/latex/qtree/}}. It
improves on TikZ's standard tree-drawing facility by laying out tree
nodes without collisions; it improves on Qtree by adding lots of
features from TikZ; and it improves on \verb|pst-qtree| in being
usable with pdf\TeX{} and
\XeTeX{}.

\section{Basics}

To load the package in \LaTeX{}:
\begin{Verbatim}
\usepackage{tikz}
\usepackage{tikz-qtree}
\end{Verbatim}
%
The simplest usage is identical to Qtree:
\begin{center}
\begin{SideBySideExample}
\Tree [.S [.NP [.Det the ] [.N cat ] ] 
          [.VP [.V sat ] 
               [.PP [.P on ] 
                    [.NP [.Det the ] [.N mat ] ] ] ] ]
\end{SideBySideExample}
\end{center}
Subtrees are delimited by square brackets. A subtree's root label is
joined by a dot (\verb|.|) to its opening bracket.\footnote{You can
also write the label after the closing bracket instead of the opening
bracket, or both, or neither. Please see the Qtree documentation for
details.} As in Qtree, spaces are required after every (internal or
leaf) node label. 

\verb|\Tree| works inside or outside a
\verb|tikzpicture| environment, but many of the features described 
below require the explicit \verb|tikzpicture| environment.

\goodbreak

\paragraph{Options} Some options for standard TikZ trees work for \verb|\Tree| as
well:
\begin{itemize}
\item \verb|level distance|: vertical distance between the anchors of a parent and its children
\item \verb|sibling distance|: horizontal distance between the boundaries of sister subtrees (not the anchors of their roots, as in standard TikZ trees). Note that TikZ nodes already have some horizontal space around them (\verb|inner xsep|, by default \verb|0.3333em|), so even \verb|sibling distance=0pt| leaves some room.
\end{itemize}
These are set either by writing
\verb|\tikzset{|\textit{option}\verb|=|\textit{value}\verb|}| or by
writing \verb|[|\textit{option}\verb|=|\textit{value}\verb|]| after a
\verb|\begin{tikzpicture}| or \verb|\begin{scope}|.\footnote{Allowing
options after \verb|\Tree| would have made sense, but there would be
no way to disambiguate the two uses of square brackets.} For example:

\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\tikzset{level distance=72pt}
\Tree [.NP [.Adj tall ] [.N tree ] ]
\end{tikzpicture}
%
\begin{tikzpicture}[sibling distance=72pt]
\Tree [.NP [.Adj fat ] [.N tree ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}

The \verb|grow=|\textit{direction}\/ and \verb|grow'=|\textit{direction}\/ options control the orientation of trees just as for standard TikZ trees. However, \textit{direction}\/ must be one of \verb|up|, \verb|down|, \verb|left|, or \verb|right|. The difference between \verb|grow| and \verb|grow'| is that \verb|grow| places children counterclockwise with respect to their parent and \verb|grow'| places them clockwise:
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}[grow'=down]
\Tree [.NP [.Adj reverse ] [.N tree ] ]
\end{tikzpicture}
%
\begin{tikzpicture}[grow'=up]
\Tree [.NP [.Adj upside-down ] [.N tree ] ]
\end{tikzpicture}
\end{SideBySideExample}
\vspace{3ex}
\begin{SideBySideExample}
\begin{tikzpicture}[grow=left]
\tikzset{level distance=60pt,sibling distance=18pt}
\tikzset{execute at begin node=\strut}
\Tree [.NP [.Adj sideways ] [.N tree ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}
Note that in sideways trees, \verb|level distance| is horizontal and \verb|sibling distance| is vertical. Sideways trees do take a little extra adjusting to look right, since the defaults are geared towards vertically growing trees. The meaning of the option \verb|execute at begin node=\strut| is, before typesetting the label of every node, insert the command \verb|\strut|, which is an invisible box that maximizes the height and depth of the node.

\paragraph{Styles} TikZ lets you define \emph{styles}\/ which encapsulate multiple options:
\begin{Verbatim}
\tikzset{small/.style={level distance=20pt,sibling distance=0pt}}
\end{Verbatim}
Then the option \verb|small| causes the options in its definition to be used:
\begin{center}
\tikzset{small/.style={level distance=20pt,sibling distance=0pt}}
\begin{SideBySideExample}
\begin{tikzpicture}[small]
\Tree [.NP [.Adj small ] [.N tree ] ]
\end{tikzpicture}
%
\begin{tikzpicture}
\Tree [.NP [.Adj normal ] [.N tree ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}
The following TikZ styles are automatically applied inside trees,
providing a hook for you to change the appearance of particular kinds
of tree parts:
\begin{itemize}
\item \verb|every tree node| to every (internal and leaf) node (default: \verb|anchor=base|)
\item \verb|every internal node| to every internal node
\item \verb|every leaf node| to every leaf node
\item \verb|edge from parent| to every edge (default: \verb|draw|)
\end{itemize}

The options for nodes and edges are all handled by TikZ and are
described in detail in the TikZ documentation. For example, if you
have a font named \verb|\ar| and want to set all the leaf labels in
this font:
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\tikzset{grow'=down}
\tikzset{every leaf node/.style={font=\ar}}
\Tree [.S [.NP القط ] 
          [.VP [.V وجلس ] 
               [.PP [.P على ] [.NP حصيرة ] ] ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}

You can make the nodes in a sideways tree line up on their left edge using \verb|anchor=base west|:
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\tikzset{grow'=right,level distance=32pt}
\tikzset{execute at begin node=\strut}
\tikzset{every tree node/.style={anchor=base west}}
\Tree [.S [.NP [.Det the ] [.N cat ] ] 
          [.VP [.V sat ] 
               [.PP [.P on ] 
                    [.NP [.Det the ] [.N mat ] ] ] ] ]
\end{tikzpicture}                    
\end{SideBySideExample}
\end{center}

In Qtree, it was allowed to use a line break (\verb|\\|) inside a node, but TikZ nodes by default don't allow this. You can enable it like so:
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\tikzset{every tree node/.style={text width=2em,text centered}}
\Tree [.S [.NP Det\\the N\\cat ]
          [.VP V\\sat
               [.PP P\\on
                    [.NP Det\\the N\\mat ] ] ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}
The downside is that you must specify a fixed node width. In the next release of TikZ, it will be possible to use instead a new \verb|align=center| option without the fixed width.\footnote{Thanks to Alan Munn for figuring this out.}

You can also define a style for all the edges in a tree. For example, if you want the edges to be a little darker:
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\tikzset{edge from parent/.style={draw,thick}}
\Tree [.S [.NP [.Det the ] [.N cat ] ] 
          [.VP [.V sat ] 
               [.PP [.P on ] 
                    [.NP [.Det the ] [.N mat ] ] ] ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}
The \verb|draw| option is necessary, as by default they will not be
drawn. As a more complex example, edges have an
\verb|edge from parent path| option which lets you change the shape of
the edge. Its value is a TikZ path expressed in terms of
\verb|\tikzparentnode|, the parent node, and \verb|\tikzchildnode|,
the child node.
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\tikzset{edge from parent/.style=
  {draw,
   edge from parent path={(\tikzparentnode.south) 
                          -- +(0,-8pt) 
                          -| (\tikzchildnode)}}} 
\Tree [.S [.NP [.Det the ] [.N cat ] ] 
          [.VP [.V sat ] 
               [.PP [.P on ] 
                    [.NP [.Det the ] [.N mat ] ] ] ] ]
\end{tikzpicture}                    
\end{SideBySideExample}
\end{center}

\clearpage

\section{Embedding TikZ nodes}

Inside a \verb|\Tree|, in place of a node label, you can use a TikZ
\verb|\node| command.\footnote{\verb|\Tree| specifically watches out
for the token \verb|\node|; do not use \verb|\path node| or other
equivalents.}
\begin{quote}
\verb|\node [|\textit{options}\verb|] (|\textit{name}\verb|) {|\textit{label}\verb|};|
\end{quote}
Don't forget the terminating semicolon. The
\verb|[|\textit{options}\verb|]|, which are optional, let you change
the appearance of the node; for example, the \verb|draw| option draws
a border around the node. The \verb|(|\textit{name}\verb|)|, which is
also optional, can be used for drawing lines/arrows to/from the node.
\begin{center}
\begin{Example}
\begin{tikzpicture}
\Tree [.CP [.NP \node(wh){what}; ] 
           [.C$'$ [.I did ] 
                  [.\node[draw]{IP}; 
                    [.NP [.Det the ] [.N cat ] ]
                    [.VP [.V sit ] 
                         [.PP [.P on ] 
                              [.\node[draw]{NP}; 
                                [.NP [.Det a ] [.N book ] ] 
                                [.PP [.P about ] [.NP \node(t){$t$}; ] ] ] ] ] ] ] ]
\draw[semithick,->] (t)..controls +(south west:5) and +(south:5) .. (wh);
\end{tikzpicture}
\end{Example}
\end{center}

You can also refer to the whole subtree rooted at the node named \textit{name}\/ using \verb|\subtreeof{|\textit{name}\verb|}|:
\begin{center}
\begin{SideBySideExample}
\begin{tikzpicture}
\Tree [.S [.NP [.Det the ] [.N cat ] ] 
          [.\node(site){VP}; [.V sat ] ] ]
\begin{scope}[shift={(1in,0.5in)}]
\Tree [.\node(root){VP}; VP$^\ast$
                         [.PP [.P on ] 
                              [.NP [.Det the ] [.N mat ] ] ] ]

\end{scope}

\draw[->](\subtreeof{root}.140) .. 
  controls +(west:1) and +(east:1) .. (site);

\end{tikzpicture}
\end{SideBySideExample}
\end{center}

\noindent Another example for machine translation people:
\begin{center}
\fvset{formatcom=\javerbfont}
\begin{SideBySideExample}
\begin{tikzpicture}
\Tree [.S [.NP [.Det \node(e1){the}; ] 
               [.N \node(e2){cat}; ] ] 
          [.VP [.V \node(e3){sat}; ] 
               [.PP [.P \node(e4){on}; ] 
                    [.NP [.Det \node(e5){the}; ] 
                         [.N \node(e6){mat}; ] ] ] ] ]

\begin{scope}[yshift=-5in,grow'=up]
\tikzset{every leaf node/.style={font=\ja}}
\Tree [.S [.NP \node(j1){猫が}; ] 
          [.VP [.PP [.NP [.NP \node(j2){マット}; ] 
                         [.Part \node(j3){の}; ]
                         [.NP \node(j4){上}; ] ] 
                    [.P \node(j5){に}; ] ] 
               [.V \node(j6){土}; ] ] ]
\end{scope}

\begin{scope}[dashed]
\draw (e1)--(j1);
\draw (e2)--(j1);
\draw (e3)..controls +(south:5) and +(north:4)..(j6);
\draw (e4)--(j4);
\draw (e4)--(j5);
\draw (e5)--(j2);
\draw (e6)--(j2);
\end{scope}

\end{tikzpicture}
\end{SideBySideExample}
\end{center}

\section{Explicit edges}

The edge from a parent to a child node is normally automatically drawn
for you, but you can do it yourself with an \verb|\edge| command
\emph{before}\/ the corresponding child node. It is similar to the
TikZ \verb|edge from parent| command.\footnote{Except that a TikZ
\texttt{edge from parent} comes after the child node. I thought it was
more logical to put it before.}
\begin{quote}
\verb|\edge [|\textit{options}\verb|];|
\end{quote}
Again, don't forget the semicolon. The
\verb|[|\textit{options}\verb|]|, which are optional, let you change
the appearance of the edge. You can also add an edge label:
\begin{quote}
\verb|\edge [|\textit{options}\verb|] node [|\textit{options}\verb|] {|\textit{label}\verb|};|
\end{quote}
Typically one will use the \verb|auto| option for edge labels, which
places the label to the side of the edge.
\begin{center}
\begin{SideBySideExample}[xrightmargin=1.25in]
\newcommand{\initial}[1]{\ensuremath{\alpha_{\textrm{\scriptsize #1}}}}
\newcommand{\auxiliary}[1]{\ensuremath{\beta_{\textrm{\scriptsize #1}}}}

\begin{tikzpicture}[level distance=36pt,sibling distance=12pt]
\Tree [.\initial{sat} 
        \edge node[auto=right]{1}; \initial{cat} 
        \edge[dashed] node[auto=left]{2}; 
        [.\auxiliary{on} 
          \edge node[auto=left]{2}; \initial{mat} ] ]
\end{tikzpicture}
\end{SideBySideExample}
\end{center}
The fact that \verb|auto=left| draws a label on the right and
\verb|auto=right| draws a label on the left makes sense if you think
about the tree growing from the root to the leaves.

There is a predefined style that draws a ``roof'' over a node, like Qtree's \verb|\qroof|:
\begin{center}
\begin{Example}
\begin{tikzpicture}[level distance=36pt]
\Tree [.S [.NP [.N this ] ] 
          [.VP [.V is ] 
               [.NP \edge[roof]; {a noun phrase 
                                  the complexity of which 
                                  is too great for me to parse} ] ] ]
\end{tikzpicture}
\end{Example}
\end{center}

\section{Qtree compatibility}

For basic trees, \tikztree{} can be used as a drop-in replacement for Qtree, but most of Qtree's advanced features are either not accessed in the same way in \tikztree{} or not implemented at all. There is a package \verb|tikz-qtree-compat| which can be loaded to improve compatibility. Supported so far are:
\begin{itemize}
\item Superscripts and subscripts outside of math mode, and \verb|\automath|
\item The \verb|\0|, \verb|\1|, and \verb|\2| commands, and \verb|\qtreeprimes|
\item The \verb|\qroof| command
\end{itemize}
For unsupported commands, warning messages are printed, but at least your file should compile.

\section*{Acknowledgements}
This was all Dan Gildea's idea. Thanks to Alan Munn for his very helpful suggestions.

\section*{Contact}
Please send suggestions to \verb|chiang@isi.edu|.

\end{document}