code: def _build_network(self):
      if self.gflu_stages > 0:
          self.gflus = GatedFeatureLearningUnit(
              n_features_in=self.n_features,
              n_stages=self.gflu_stages,
              feature_mask_function=self.feature_mask_function,
              dropout=self.gflu_dropout,
              feature_sparsity=self.gflu_feature_init_sparsity,
              learnable_sparsity=self.learnable_sparsity,
          )
      if self.num_trees > 0:
          self.trees = nn.ModuleList(
              [
                  NeuralDecisionTree(
                      depth=self.tree_depth,
                      n_features=self.n_features
                      + 2**self.tree_depth * t
                      if self.chain_trees
                      else self.n_features,
                      dropout=self.tree_dropout,
                      binning_activation=self.binning_activation,
                      feature_mask_function=self.feature_mask_function,
                      feature_sparsity=self.tree_feature_init_sparsity,
                      learnable_sparsity=self.learnable_sparsity,
                  )
                  for t in range(self.num_trees)
              ]
          )
          if self.tree_wise_attention:
              self.tree_attention = nn.MultiheadAttention(
                  embed_dim=self.output_dim,
                  num_heads=1,
                  batch_first=False,
                  dropout=self.tree_wise_attention_dropout,
              )
  
imports: import torch
  import torch.nn
  from omegaconf import DictConfig
  from pytorch_tabular.models.common.heads import blocks
  from pytorch_tabular.models.common.layers import Add, Embedding1dLayer, GatedFeatureLearningUnit, NeuralDecisionTree
  from pytorch_tabular.models.common.layers.activations import entmax15, entmoid15, sparsemax, sparsemoid, t_softmax
  from pytorch_tabular.utils import get_logger
  from ..base_model import BaseModel
label_desc: Use image node_id 2 for calling the GatedAdditiveTreesBackbone obj's underlying member method code with example usage: obj._build_network() without return types