code: def depth(self):
          
          cat = self._xChart.cat
          if cat is None:
              return 0
          if cat.multiLvlStrRef is None:
              return 1
          return len(cat.lvls)
docs: Return an integer representing the number of hierarchical levels in
          this category collection. Returns 1 for non-hierarchical categories
          and 0 if no categories are present (generally meaning no series are
          present).