Herewith an (barebones) Expandable (DropDown) List example using CompCreator. Each item is a horizontal arrangement with a label for the test. The sublists are in vertical arrangements.
The "fun" part was working out the logic for the click event for the top level list items.
This could be expanded (pun intended) for additional sub levels, but you will need your thinking cap on for that.
This could also be made much prettier, make it look like a cardview list, add list item icons, and drop down icon for those elements that have sublists.
AIA
expandableLists.aia (41.7 KB)
VIDEO