Q:

Putting a tree next to another tree

How can I put example tree (a) and example tree (b) next to each other on the page? At the moment, tree (b) appears below tree (a):
\documentclass[12pt,a4paper]{article}   
\usepackage{tikz-qtree}
\usepackage{tikz-qtree-compat}
\usepackage{ulem}

\begin{document}
\ex. \a. \begin{tikzpicture} \Tree [.DP [.N Pat ] ] \end{tikzpicture} 
\b.  \label{VP} \begin{tikzpicture}
\Tree [.VP  [.V saw ] [.DP [.N Kim ] ]]
\end{tikzpicture}

\end{document}

A:

You can use a multicols environment from multicol package.
The example below shows your original tikz-qtree code and a version using the  powerful forest package; in both cases, alignment was improved using the baseline option:

The code:
\documentclass[12pt,a4paper]{article}   
\usepackage{tikz-qtree}
\usepackage{tikz-qtree-compat}
\usepackage{ulem}
\usepackage{linguex}
\usepackage{multicol}
\usepackage{forest}

\begin{document}
\begin{multicols}{2}

\ex. 
\a. \begin{tikzpicture}[baseline] \Tree [.DP [.N Pat ] ] \end{tikzpicture}
\b.  \label{VP} \begin{tikzpicture}[baseline]
\Tree [.VP  [.V saw ] [.DP [.N Kim ] ]]
\end{tikzpicture}

\end{multicols}

\begin{multicols}{2}

\ex. 
\a. 
\begin{forest}
baseline 
[DP 
  [N 
    [Pat]
  ]   
] 
\end{forest}
\b.  \label{VP} 
\begin{forest}
baseline
[VP  
  [V
    [saw] 
  ]
  [DP
    [N
      [Kim] 
    ]
  ]
]
\end{forest}

\end{multicols}

\end{document}

