code: def _assemble_child_tree(self, tree, child_id):
      for child in tree["children"]:
          if child["nodeid"] == child_id:
              return self._assemble_tree(child)
      assert False, f"Unexpected child ID: {child_id}"
  
imports: import json
  import math
  import numpy
  from m2cgen import ast
  from m2cgen.assemblers import utils
  from m2cgen.assemblers.base import ModelAssembler
  from m2cgen.assemblers.linear import _linear_to_ast
label_desc: Use image node_id 3 for calling the XGBoostTreeModelAssembler obj's underlying member method code with example usage: obj._assemble_child_tree(tree, child_id) and returns: self