\documentclass{article}
\usepackage{pst-tree}
\makeatletter
\newcount\@Bernoudepth
\newcount\@Bernoumaxdepth
\newcommand\Bernoutree[8][treemode=R,nodesep=1ex,levelsep=12ex]{%
\begingroup
\psset{treemode=R,nodesep=1ex,levelsep=12ex} \psset{#1} \@Bernoumaxdepth #2\relax
\def\@Reussite{#3} \def\@Echec{#4} \def\@probareussite{#5} \def\@Argreussite{#6} \ifx\empty\@Argreussite
\def\@Argreussite{0.5} \fi
\def\@probaechec{#7} \def\@Argechec{#8}
\ifx\empty\@Argechec
\def\@Argechec{0.5} \fi
\pstree{\TR{}}{\@Bernoutree{1}}
\endgroup
}
\newcommand\@Bernoutree[1]{%
\@Bernoudepth #1\relax
\ifnum\@Bernoudepth=\@Bernoumaxdepth
\TR{\@Reussite}\taput[tpos=\@Argreussite]{\@probareussite}
\TR{\@Echec}\tbput[tpos=\@Argechec]{\@probaechec}
\else
\advance\@Bernoudepth \@ne
\pstree{\TR{\@Reussite}\taput[tpos=\@Argreussite]
{\@probareussite}}{\@Bernoutree{\the\@Bernoudepth}}
\pstree{\TR{\@Echec}\tbput[tpos=\@Argechec]
{\@probaechec}}{\@Bernoutree{\the\@Bernoudepth}}
\fi
}
\makeatother
\pagestyle{empty}
\begin{document}
\Bernoutree{3}{$A$}{$\bar{A}$}{$p$}{0.4}{$1-p$}{0.2}
\Bernoutree[levelsep=18ex,treenodesize=0pt]{4}{$R$}{$E$}{$p$}{}{$q$}{}
\end{document}