Dropdown (sub-item) menu - Clubs

We are using the Club function to create a space for a number of static pages (related to hospital support in Ukraine: https://99nicu.org/clubs/5-support-nicus-in-ukraine/).

It would be great to be able to create sub-items in the menu, i.e. like a dropdown function. In the example above, we would like to group pages this way, to avoid too many items in the "main menu".