code: def linear_model_tree(X, y):
      regr = LinearTreeRegressor(
          LinearRegression(), criterion="mse", max_depth=5
      )
      regr.fit(X, y)
      return regr
  
imports: import numpy
  import pyomo.environ
  import pytest
  from omlt.dependencies import lineartree_available
  from pytest import approx
  from omlt import OmltBlock
  import omlt
label_desc: Use image node_id 1 for calling a global function with example usage: linear_model_tree(X, y) and returns: regr