og_sm-8.x-1.0/og_sm_admin_menu/og_sm_admin_menu.site_links.menu.yml

og_sm.site.admin:
  title: 'Administer site'
  route_name: entity.node.og_admin_routes
  menu_name: og_sm_admin_menu
og_sm.site.structure:
  title: 'Structure'
  route_name: og_sm.site.structure
  parent: og_sm.site.admin
  menu_name: og_sm_admin_menu
  weight: 30
  options:
    attributes:
      class:
        - 'toolbar-icon-system-admin-structure'