Mobile menu with expandable submenus

Hi,

I am pretty new to all the wordpress stuff, but I already like how Tiny Framework is organized and all of that. However, I have one little problem: In the mobile view I would like to have a menu with drop-down (or expandable) submenu entries, so that you don’t have to look at all of the menu and sub-menu entries at once and scroll all the way through them to reach a specific page.

To give you a little example of what I mean:
https://twentyfifteendemo.wordpress.com/
This twentyfifteen example page in mobile view gives you the menu entry “A parent page”. If you click on the arrow the sub-menu expands giving you all the sub-pages of that entry.
http://mtomas.com/
The Tiny Framework page in mobile view however gives you all the sub-menus already expanded, presenting a rather long list (which can be even longer for certain web sites).

I would like to know if (and how) it would be possible to have a mobile menu with expandable sub-menus in Tiny Framework.

Thank you for your help and your great work!