Zum Spaß mit TikZ `graphdrawing`.
    \documentclass{article}
    \usepackage{tikz}
    \usetikzlibrary{graphs,graphdrawing}
    \usegdlibrary{trees}
    \begin{document}
    \begin{tikzpicture}
      \graph [trie,tree [fresh nodes,tree layout] {
        "@" -> {
          "@" -> {
            "$\lambda$" -> {
              "x", "$\mathrm{case_{List}}$" -> {
                "x", "2", "3"
              }
            },
            "Cons" -> {
              "$\lambda$" -> {
                /"z", /"z"
"z", "z"
              },
              "Nil"
            }
          },
          "True"
        }
      };
    \end{tikzpicture}
    \end{document}
> ![alt text][1]
  [1]: http://texwelt.de/wissen/upfiles/r_53.pnghttp://texwelt.de/wissen/upfiles/r_54.png