code: def _is_first_layer(self, nodes):
      if len(nodes) == 1 and nodes[0].nid == 0:
          return True
      else:
          return False
  
imports: import typing
  import torch
  from typing import Dict
  from fate.arch.histogram import HistogramBuilder, DistributedHistogram
  from fate.ml.ensemble.learner.decision_tree.tree_core.decision_tree import Node
  from typing import List
  import numpy
  from fate.arch.dataframe import DataFrame
  from fate.arch import Context
  import logging
label_desc: Use image node_id 7 for calling the SBTHistogramBuilder obj's underlying member method code with example usage: obj._is_first_layer(nodes) and returns: True, False