\usepackage {pstricks,pst-node,pst-tree} \psset{labelsep=2pt,tnpos=a,radius=2pt} \pstree[treemode=R]{\TC*~{25}} { \TC*~{5}~[tnpos=r]{$L_a$} \taput{$a$} \pstree{\TC*~{20}\tbput{$b$}} { \pstree{\TC*~{15}\taput{$a$}} { \TC*~{7}~[tnpos=r]{$L_{baa}$}\taput{$a$} \TC*~{5}~[tnpos=r]{$L_{bab}$}\taput{$b$} \TC*~{3}~[tnpos=r]{$L_{bac}$}\tbput{$c$} } \TC*~{5}~[tnpos=r]{$L_{bb}$} \tbput{$b$} } }