code: function () {
              var self = this;
              self.renderChildren.apply(self, arguments);    // only sync child sub tree at root node
              // only sync child sub tree at root node
              if (self === self.get('tree')) {
                  updateSubTreeStatus(self, self, -1, 0);
              }
          }
docs: override root 's renderChildren to apply depth and css recursively