code: def ladderize(self, direction=0):
          
          nself = deepcopy(self)
          nself.treenode.ladderize(direction=direction)
          nself._fixed_order = None
          nself._coords.update()
          return nself
docs: Ladderize tree (order descendants) so that top child has fewer 
          descendants than the bottom child in a left to right tree plot. 
          To reverse this pattern use direction=1.