I need to draw an arrow, using \draw[semithick,->] (t)..controls +(south west:5) and +(south:5) .. (wh);.
I want the arrow to connect e3 at the bottom of the following tree to the single e3 occurring higher up in it:
\documentclass[12pt,a4paper]{article}
\usepackage{tikz-qtree}
\usepackage{tikz-qtree-compat}
\usepackage{ulem}
\begin{document}
\begin{tikzpicture}
\Tree [.{$<$t$_{1}$,\hspace{0.1cm} \\$\lbrack$ \hspace{0.3cm} $\rbrack$, $\lbrack$ \hspace{0.3cm} $\rbrack$ $>$} [.{$<$(e$_{3}$ $\rightarrow$ t$_{1}$) $\rightarrow$ t$_{1}$),\hspace{0.1cm} \\$\lbrack$ e$_{3}$ $\rbrack$ $>$} \node(wh){something} ;]
[.{$<$(e$_{3}$ $\rightarrow$ t$_{1}$), \hspace{0.1cm} \\$\lbrack$ e$_{2}$ $\rbrack$, \hspace{0.1cm} \\$\lbrack$ \hcancel{e$_{3}$}
\thinspace $\rbrack$ $>$ } [.{e$_{3}$} ]
[.\node[draw]{{$<$t$_{1}$, \hspace{0.1cm} \\$\lbrack$ e$_{2}$ $\rbrack$, \hspace{0.1cm} \\$\lbrack$ e$_{3}$ $\rbrack$ $>$ }};
[.\node[draw]{e$_{2}$ }; ]
[.{$<$(e$_{2}$ $\rightarrow$ t$_{1}$), \hspace{0.1cm} \\$\lbrack$ e$_{3}$ $\rbrack$ $>$} [.{$<$(e$_{3}$ $\rightarrow$ e$_{2}$ $\rightarrow$ t$_{1}$),\hspace{0.1cm} \\$\lbrack$ $\emptyset$ $\rbrack$ $>$} {$<$(e$_{3}$ $\rightarrow$ e$_{2}$ $\rightarrow$ t$_{1}$),\hspace{0.1cm} \\$\lbrack$ $\emptyset$ $\rbrack$ $>$} ]
[.\node[draw]{e$_{3}$ };
[. e$_{3}$; ] ] ] ] ] ] ] ]
\end{tikzpicture}
\end{document}
How can I do this?

}somewhere? I can't compile this code. – Alenanno Jun 17 '15 at 09:17_is used outside math mode. I don't see a reason to keep going in and out of math mode within your type specifications. I would recommend posting a much simpler MWE (or at least a screenshot of the output you get iwth the one you posted) so we can see what's going on with the arrow. The code snippet for the arrow looks fine -- you should just be able to put that after the last bracket in the tree and before\end{tikzpicture}. – Jason Zentz Jun 17 '15 at 12:17