ERROR: problems during latex
INPUT:
\documentclass[fleqn,12pt]{article}
\usepackage{amsmath}
\usepackage[normal]{xcolor}
\setlength{\mathindent}{0cm}
\definecolor{teal}{rgb}{0,0.5,0.5}
\definecolor{navy}{rgb}{0,0,0.5}
\definecolor{aqua}{rgb}{0,1,1}
\definecolor{lime}{rgb}{0,1,0}
\definecolor{maroon}{rgb}{0.5,0,0}
\definecolor{silver}{gray}{0.75}
\usepackage{latexsym}
\begin{document}
\pagestyle{empty}
\pagecolor{white}
{
\color{black}
\begin{math}\displaystyle \begin{parsetree}
    ( .S. 
        (.NP.  `we')
        ( .VP.
            (.V.    `gave' )
            (.NP.   `them')
            (.NP. ~ `a toy')
         )
    )
\end{parsetree}\end{math}
}
\clearpage
\end{document}
STDERR:
This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian)
entering extended mode
(/tmp/wVWn5g2or8/WjPVrfGx1f
LaTeX2e <2009/09/24>
Babel  and hyphenation patterns for english, usenglishmax, dumylang, noh
yphenation, loaded.
(/usr/share/texmf-texlive/tex/latex/base/article.cls
Document Class: article 2007/10/19 v1.4h Standard LaTeX document class
(/usr/share/texmf-texlive/tex/latex/base/fleqn.clo)
(/usr/share/texmf-texlive/tex/latex/base/size12.clo))
(/usr/share/texmf-texlive/tex/latex/amsmath/amsmath.sty
For additional information on amsmath, use the `?' option.
(/usr/share/texmf-texlive/tex/latex/amsmath/amstext.sty
(/usr/share/texmf-texlive/tex/latex/amsmath/amsgen.sty))
(/usr/share/texmf-texlive/tex/latex/amsmath/amsbsy.sty)
(/usr/share/texmf-texlive/tex/latex/amsmath/amsopn.sty))
(/usr/share/texmf/tex/latex/xcolor/xcolor.sty
(/etc/texmf/tex/latex/config/color.cfg)
(/usr/share/texmf-texlive/tex/latex/graphics/dvips.def))
(/usr/share/texmf-texlive/tex/latex/base/latexsym.sty)
No file WjPVrfGx1f.aux.
(/usr/share/texmf-texlive/tex/latex/base/ulasy.fd)

! LaTeX Error: Environment parsetree undefined.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H   for immediate help.
 ...                                              
                                                  
l.17 \begin{math}\displaystyle \begin{parsetree}
                                                

! LaTeX Error: \begin{math} on input line 17 ended by \end{parsetree}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H   for immediate help.
 ...                                              
                                                  
l.26 \end{parsetree}
                    \end{math}
[1] (./WjPVrfGx1f.aux) )
(see the transcript file for additional information)
Output written on WjPVrfGx1f.dvi (1 page, 612 bytes).
Transcript written on WjPVrfGx1f.log.