\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}