code: def add_child(self, tree):
          '''Add a child to the list of this tree's children
  
          This tree becomes the added tree's parent
          '''
          tree.parent = self
          self.children.append(tree)
          return tref add_child(self, tree):
          '''Add a child to the list of this tree's children
  
          This tree becomes the added tree's parent
          '''
          tree.parent = self
          self.children.append(tree)
          return tree
docs: Add a child to the list of this tree's children
  
          This tree becomes the added tree's parent