    +-----+-----+       ++-+   +--+--+   
  |     |        |           |       |  |   |     |   
MS.a  MS.p      E.a         E.p      4  4   3     3   
              +--+--+     +--+--+          ++-+  ++-+ 
              |     |     |     |          |  |  |  | 
            E.al  E.ar  E.pl  E.pr         4  4  4  4 
</pre><p><b><tt>treefun2</tt></b> does the same, but with two trees and a 2-arguments function:</p><pre class="codeinput">lastLetter = t.treefun2(letterCount, @(a, b) a(b));
disp(lastLetter.tostr