\savebox{\arbreSave}{\input{figures/arbres_pw/arbre12}}
{ \newcommand{\nodea}{\node[draw,circle] (a) {$$}
;}\newcommand{\nodestara}{\node (sa) {$\bigstar$}
;}\newcommand{\nodeb}{\node (b) {$\usebox{\arbreSave}$}
;}\begin{tikzpicture}[auto]
\matrix[column sep=.3cm, row sep=.3cm,ampersand replacement=\&]{
         \& \nodea     \\ 
  \nodeb \& \nodestara \\ 
};

\path[ultra thick, red] (a) edge (b);
\end{tikzpicture}}