code: def debug_print(self):
          '''Print tree'''
  
          def print_node(node, depth=0):
              print('{}{}'.format('  ' * depth, repr(node)))
              if node.is_container():
                 for child in node.children:
                     print_node(child, depth + 1)
  
          for root in self.stack:
              print_node(rootf debug_print(self):
          '''Print tree'''
  
          def print_node(node, depth=0):
              print('{}{}'.format('  ' * depth, repr(node)))
              if node.is_container():
                 for child in node.children:
                     print_node(child, depth + 1)
  
          for root in self.stack:
              print_node(root)
docs: Print tree