You can multiple links in the same way that you add one link.
This creates a front page link on a menu for anonymous users and a front page link on a menu for authenticated users, as well as a parent and child menu link (Fruits -> Apple) for anonymous users.
MYMODULE.links.yml
:
MYMODULE.anon-home:
title: 'Home'
route_name: 'entity.node.canonical'
route_parameters: { node: '1' }
weight: 0
menu_name: main-navigation-anon
MYMODULE.anon-fruits:
title: 'Fruits'
route_name: 'entity.node.canonical'
route_parameters: { node: '4' }
weight: 10
menu_name: main-navigation-anon-ja
MYMODULE.anon-apples:
title: 'Apples'
route_name: 'entity.node.canonical'
route_parameters: { node: '6' }
parent: MYMODULE.anon-fruits
weight: 0
menu_name: main-navigation-anon-ja
MYMODULE.auth-home:
title: 'Home'
route_name: 'entity.node.canonical'
route_parameters: { node: '1' }
weight: 0
menu_name: main-navigation-auth