Custom menus in the new Backoffice

Questions
,
8

So, I should probably upgrade to Umbraco 16? (currently using 15)

If I create a sidebar App like this

const sidebarApp: UmbExtensionManifest = {
    type: "sectionSidebarApp",
    kind: "menu",
    alias: "LC.Settings.Sidebar",
    name: "LC Settings Sidebar",
    weight: 1000,
    meta: {
        label: "LC",
        menu: MENU_ALIAS,
    },
    conditions: [{
        alias: "Umb.Condition.SectionAlias",
        match: SECTION_ALIAS,
    }],
};

const settingsMenuItem: UmbExtensionManifest = {
    type: 'menuItem',
    alias: 'LC.Settings.MenuItem',
    name: 'LC Settings Item',
    weight: 100,
    meta: {
       label: 'LC',
       icon: 'icon-folder',
       menus: [MENU_ALIAS]
    }
};

const menu: UmbExtensionManifest = {
    type: "menu",
    alias: MENU_ALIAS,
    name: "LC Settings Menu",
    meta: {
        menuItems: [settingsMenuItem.alias]
    }
};

How do I then make a custom tree appear under the “LC” top level menu?