code: def height(self):
          
  
          min_height = int(bool(self))
          return max([min_height] + [c.height()+1 for c, p in self.children])
docs: Returns height of the (sub)tree, without considering
          empty leaf-nodes
  
          >>> create(dimensions=2).height()
          0
  
          >>> create([ (1, 2) ]).height()
          1
  
          >>> create([ (1, 2), (2, 3) ]).height()
          2