侧边栏如何增加多级菜单

目前侧边栏只支持到第一级和第二级的展开，如何增加到第三级和第四级呢？
我在router.js中的appRouter已经给需要第三级目录的对象添加了children字段，但是浏览器会报错。
请问一下正确添加菜单的姿势？希望得到作者的回复。

Start with router.js and the appRouter configuration, then reproduce the browser error after adding children to a third-level menu item. Trace the existing first- and second-level sidebar handling and determine what would need to support third- and fourth-level menus; done means nested menus render without the reported error.

Written by the indexing model from the issue text.