code: def build_tree(self, *args, **kwargs):
          
          # Check length #
          assert len(self) > 3
          # Default option #
          algorithm = kwargs.pop(kwargs, None)
          if algorithm is None: algorithm = 'raxml'
          # Dispatch #
          if algorithm is 'raxml':    return self.build_tree_raxml(*args, **kwargs)
          if algorithm is 'fasttree': return self.build_tree_fast(*args, **kwargs)
docs: Dispatch a tree build call. Note that you need at least four
          taxa to express some evolutionary history on an unrooted tree.