code: def _init_sample_pos(self, train_data: DataFrame):
      sample_pos = train_data.create_frame()
      sample_pos["node_idx"] = 0  # position of current sample
      return sample_pos
  
imports: import numpy
  import pandas
  from fate.arch import Context
  from fate.arch.dataframe import DataFrame
  from fate.ml.ensemble.learner.decision_tree.tree_core.splitter import SplitInfo
  from typing import List
  import logging
label_desc: Use image node_id 2 for calling the DecisionTree obj's underlying member method code with example usage: obj._init_sample_pos(train_data) and returns: sample_pos