code: function (el) {
          if (el.__storage === this) {
              return;
          }
  
          if (el instanceof Group) {
              el.addChildrenToStorage(this);
          }
  
          this.addToStorage(el);
          this._roots.push(el);
      }
docs: 添加图形(Shape)或者组(Group)到根节点
  @param {module:zrender/Element} el