code: def gen_masked_tree(self, node, mask_token, depth=1):
      if self.should_mask(depth):
          actual_str_len = len(node.flat_str().strip().split(" "))
          return " ".join([mask_token for idx in range(actual_str_len)])
      else:
          return_str = " "
          if (
              isinstance(node, Intent)
              or isinstance(node, Slot)
              or isinstance(node, Root)
          ):
              return_str += "["
              return_str += node.label
              return_str += " "
              for child in node.children:
                  return_str += self.gen_masked_tree(
                      child, mask_token, depth + 1
                  )
                  return_str += " "
              return_str += "]"
          else:
              return_str += node.label
              return_str += " "
          return return_str.strip()
  
imports: from typing import Dict, List, Optional, Set
  import numpy
  from pytext.common.constants import SpecialTokens, Token
  from pytext.config.component import Component, ComponentType
  from pytext.config.pytext_config import ConfigBase
  from pytext.data.data_structures.annotation import Annotation, Intent, Root, Slot
  from pytext.data.utils import VocabBuilder, Vocabulary
label_desc: Use image node_id 4 for calling the TreeMask obj's underlying member method code with example usage: obj.gen_masked_tree(node, mask_token, depth) and returns: str, return_str