code: def hybrid_forward(self, F, x, residual=None, children=None):
      children = [] if children is None else children
      bottom = self.downsample(x)
      residual = self.project(bottom)
      if self.level_root:
          children.append(bottom)
      x1 = self.tree1(x, residual)
      if self.levels == 1:
          x2 = self.tree2(x1)
          x = self.root(x2, x1, *children)
      else:
          children.append(x1)
          x = self.tree2(x1, None, children)
      return x
  
imports: from __future__ import division
  import os
  import mxnet
  from mxnet.gluon.block import HybridBlock
  from mxnet.gluon import nn
  from mxnet.gluon.nn import BatchNorm
label_desc: Use image node_id 2 for calling the Tree obj's underlying member method code with example usage: obj.hybrid_forward(F, x, residual, children) and returns: x