[Vuejs]-How to make sidebar with children elements in Vitepress?

Ok, as of vitepress version 1.0.0-alpha.61 this is the correct way of configuring a collapsible multi-layer sidebar:

sidebar: [
    {
      text: 'Group 1',
      items: [
        {
          text: 'Group 2',
          collapsed: true,
          items: [
            { text: 'blub1', link: '/group1/page1.md' },
            { text: 'blub2', link: '/group1/page2.md' },
          ],
        },
      ],
    },
    {
      text: 'Group 2',
      collapsed: true,
      items: [
        { text: 'blub1', link: '/group2/page1.md' },
        { text: 'blub2', link: '/group2/page2.md' },
      ],
    },
],

source: https://vitepress.dev/reference/default-theme-sidebar#collapsible-sidebar-groups