Fix style

Author: santisoler

discretize/tree_mesh.py

@@ -92,12 +92,17 @@
 from discretize.base import BaseTensorMesh
 from discretize.operators import InnerProducts, DiffOperators
 from discretize.mixins import InterfaceMixins, TreeMeshIO
-from discretize._extensions.tree_ext import _TreeMesh, TreeCell, TreeMeshNotFinalizedError  # NOQA F401
+from discretize._extensions.tree_ext import (  # noqa: F401
+    _TreeMesh,
+    TreeCell,
+    TreeMeshNotFinalizedError,
+)
 import numpy as np
 import scipy.sparse as sp
 from discretize.utils.code_utils import deprecate_property
 from scipy.spatial import Delaunay
 
+
 class TreeMesh(
     _TreeMesh,
     InnerProducts,