How could I draw an arrow to the right of the dotted circle and write some text after it, e.g. -> /a/?
\documentclass[a4paper,12pt]{beamer}
\usepackage{tikz-qtree}
\begin{document}
\begin{tikzpicture}[scale=0.6]
\tikzset{sibling distance=5em}
\draw[blue, dotted] (-.5,-2.2) circle (40pt);
\node (top) {}
child[blue] {node {$\phi$}}
child [blue] {node {}
child [blue]{node {T}}
child {node {}
child[red] {node {Mood}}
child [red]{node {}
child {node {Asp}}
child {node {}
child {node {Cause}}
child {node {Proc}}
}}}};
\end{tikzpicture}
\end{document}

tikz-qtreebut not using it? The basictikzmethods for trees are really not very useful compared to what you can achieve much more simply withtikz-qtreeor even better,forest. – Alan Munn Mar 22 '22 at 21:45