code: def trees(return_X_y=True):
      
      # y is real.
      # recommend InvGaussGAM, or GAM(distribution='gamma', link='log')
      trees = pd.read_csv(PATH + '/trees.csv', index_col=0)
      if return_X_y:
          y = trees.Volume.values
          X = trees[['Girth', 'Height']].values
          return _clean_X_y(X, y)
      return trees
docs: cherry trees dataset
  
      Parameters
      ----------
      return_X_y : bool,
          if True, returns a model-ready tuple of data (X, y)
          otherwise, returns a Pandas DataFrame
  
      Returns
      -------
      model-ready tuple of data (X, y)
          OR
      Pandas DataFrame
  
      Notes
      -----
      X contains the girth and the height of each tree.
      y contains the volume.
  
      Source:
      https://vincentarelbundock.github.io/Rdatasets/doc/datasets/trees.html