Show sub menu on click


I would like to have sub menu that would show when the parent item is clicked.

Right now my homepage looks like this (I don't want the url to be public):

The menu is on the left side of the page and it has four categories.

In the backend the homepage looks like this:

The menu here:

If I add sub items to the menu, then they are automatically shown in the homepage. I would like to add the sub menu items in a way that they would only show when the parent item/page is clicked. Is this possible to do somehow?

Thanks in advance!