# PSTree creates confusing Undefined control sequence

This bit of code generates an undefined control sequence on the last curly brace. What am I doing wrong?

\psset{levelsep=1cm,treesep=.75cm,nodesep=4pt}
\begin{center}

\pstree{\Tr{$z$}}
{
\pstree{\Tr{$y$}}
{
\pstree{\Tr{$w$}}
{
\Ttri{A}
\pstree{\Tr{$x$}}
{
\Ttri{B}
\Ttri{C}
}
}
\Ttri{D}
}
\Ttri{E}
}

\hspace*{0.5in}
into
\hspace*{0.5in}

\pstree{\Tr{$x$}}
{
\pstree{\Tr{$w$}}%
{
\Ttri{A}
\Ttri{B}
}
\pstree{\Tr{$y$}}
{
\Ttri{C}
\pstree{\Tr{$z$}}
{
\Ttri{D}
\Ttri{E}
}
}
}

\end{center}

-

Run the file with xetex or load the package auto-pst-pdf and then run it with pdflatex -shell-escape <file>. See also http://tug.org/PSTricks/main.cgi?file=pdf/pdfoutput
\usepackage{pst-tree}