code: def rtreeviz_bivar_heatmap(
      tree_model,
      X_train: (
          pd.DataFrame,
          np.ndarray,
      ) = None,  # dataframe with only one column
      y_train: (pd.Series, np.ndarray) = None,
      feature_names: List[str] = None,
      target_name: str = None,
      tree_index: int = None,  # required in case of tree ensemble
      ax=None,
      fontsize=10,
      ticks_fontsize=12,
      fontname="Arial",
      show={"title"},
      n_colors_in_map=100,
      colors=None,
      markersize=15,
  ) -> tree.DecisionTreeClassifier:
      """
      Show tesselated 2D feature space for bivariate regression tree. X_train can
      have lots of features but features lists indexes of 2 features to train tree with.
      """
      warnings.warn(
          "rtreeviz_bivar_heatmap() function is deprecated starting from version 2.0. \n "
          "For the same functionality, please use this code instead: \n m = dtreeviz.model(...) \n m.rtree_feature_space(...)",
          DeprecationWarning,
          stacklevel=2,
      )
  
      shadow_tree = ShadowDecTree.get_shadow_tree(
          tree_model,
          X_train,
          y_train,
          feature_names,
          target_name,
          None,
          tree_index,
      )
  
      model = DTreeVizAPI(shadow_tree)
      model.rtree_feature_space(
          ax=ax,
          fontsize=fontsize,
          ticks_fontsize=ticks_fontsize,
          fontname=fontname,
          show=show,
          n_colors_in_map=n_colors_in_map,
          colors=colors,
          markersize=markersize,
      )
  
imports: import warnings
  from numbers import Number
  from typing import Mapping, List
  import numpy
  import pandas
  from sklearn import tree
  from dtreeviz.models.shadow_decision_tree import ShadowDecTree
  from dtreeviz.utils import myround, DTreeVizRender
  from dtreeviz.trees import DTreeVizAPI
label_desc: Use image node_id 3 for calling a global function with example usage: rtreeviz_bivar_heatmap(tree_model, X_train, y_train, feature_names, target_name, tree_index, ax, fontsize, ticks_fontsize, fontname, show, n_colors_in_map, colors, markersize) without return types