code: def face_adjacency_tree(self):
          
          # the (n,6) interleaved bounding box for every line segment
          segment_bounds = np.column_stack((
              self.vertices[self.face_adjacency_edges].min(axis=1),
              self.vertices[self.face_adjacency_edges].max(axis=1)))
          tree = util.bounds_tree(segment_bounds)
          return tree
docs: An R-tree of face adjacencies.
  
          Returns
          --------
          tree: rtree.index
            Where each edge in self.face_adjacency has a
            rectangular cell