\psset{nodesep=3mm,levelsep=3cm,treesep=1.5cm}
\pstree[treemode=R]{\TC}{%
		\pstree{\TR{G} \naput{$\frac{2}{3}$}}{% 
				\pstree{\TR{G} \naput{$\frac{2}{3}$}}{% 
						\Tcircle{G} \naput{$\frac{2}{3}$}
						\Tcircle{P} \nbput{$\frac{1}{3}$}
				}
				\pstree{\TR{P} \naput{$\frac{1}{3}$}}{% 
						\Tcircle{G} \naput{$\frac{2}{3}$}
						\TR{P} \nbput{$\frac{1}{3}$}
				}
	 }
		\pstree{\TR{P} \nbput{$\frac{1}{3}$}}{% 
				\pstree{\TR{G} \naput{$\frac{2}{3}$}}{% 
						\Tcircle{G} \naput{$\frac{2}{3}$}
						\TR{P} \nbput{$\frac{1}{3}$}
				}
				\pstree{\TR{P} \naput{$\frac{1}{3}$}}{% 
						\TR{G} \naput{$\frac{2}{3}$}
						\TR{P} \nbput{$\frac{1}{3}$}
				}
		}
	 }