\documentclass[12pt]{article}

\usepackage{cm-lingmacros, lingtrees}

\begin{document}
Here is a very simple example:
\begin{example}
.[
S
   NP
     John
   VP
     V
       bit
     NP|tri
       Fido's best mate|tri
.]
\end{example}
That was easy, wasn't it?
\end{document}