def METHOD_NAME(self):
    h = np.ones(16)
    mesh = discretize.TreeMesh([h, 2 * h, 3 * h])
    cell_points = np.array([[0.5, 0.5, 0.5], [0.5, 2.5, 0.5]])
    cell_levels = np.array([4, 4])
    mesh.insert_cells(cell_points, cell_levels)
    self.mesh = mesh