Show as expanded doesn't work I am trying to make my own theme for drupal 8. but I am struggling with the menu.
my menu looks something like this

parent1
- child 1.1
- child 1.2
parent2
- child 2.1
- child 2.2


but only the parents are visible.

I used the menu.html.twig file from the classy theme.

edit:
I tried my theme on other site and there the children are displayed. so guess the problems was not because of theme. so i activated the stark theme, but also there I can't see my full menu tree. 
and the checkboxes show as expanded are checked
Make sure your parent links are set to Show as expanded on the /admin/structure/menu/manage/main page