el-tree 树形结构添加层级标识

 addTreeDataIndex(tree, index = 0) {
      return tree.map((item) => {
        const newItem = { ...item, Index: index++ };
        if (item.children) {
          newItem.children = this.addTreeDataIndex(item.children, index);
        }
        return newItem;
      });
    },