code: def print_tree(self, level=0, max_depth=None):
      print("  " * level + str(self))
      if max_depth is not None and max_depth <= level:
          return
      for child in self.children():
          child.print_tree(level + 1, max_depth=max_depth)
  
imports: from __future__ import print_function
  import timeit
  from sympy import *
label_desc: Use image node_id 11 for calling the TreeNode obj's underlying member method code with example usage: obj.print_tree(level, max_depth) without return types