code: def add_child_to_self( self, tree ):
          ''' Adds given *tree* as a child of the current tree. '''
          assert isinstance(tree, Tree), \
                 '(!) Unexpected type of argument for '+argName+'! Should be Tree.'
          if (not self.children):
              self.children = []
          tree.parent = self
          self.children.append(treef add_child_to_self( self, tree ):
          ''' Adds given *tree* as a child of the current tree. '''
          assert isinstance(tree, Tree), \
                 '(!) Unexpected type of argument for '+argName+'! Should be Tree.'
          if (not self.children):
              self.children = []
          tree.parent = self
          self.children.append(tree)
docs: Adds given *tree* as a child of the current tree.