comefrom: <doocs>1339.Maximum Product of Splitted Binary Tree_2.py
code: def sum(root):
      if root is None:
          return 0
      return root.val + sum(root.left) + sum(root.right)
masked: def sample_funcname ( var_1 ) :
      if var_1 is None :
          return 0
      return var_1.val + var_0 ( var_1.left ) + var_0 ( var_1.right )
  