\input{umtest-preamble}
\usepackage{unicode-math}
\setmathfont{Cambria Math}
\begin{document}
\[ \left[ \left[ \left[ \left[ \left[ \left[ x^2 
    \right]^2 \right]^2 \right]^2 \right]^2 \right]^2 \right] \]
\end{document}