I’ve had fair success using a Grid Panel for hierarchical menus. Up to 12 levels of indentation are available this way.
Just be sure that you always build your hierarchies from the top down. That is, your code can easily append items to the Grid Panel – append a (named) row, append a (positioned) item within a row, left-to-right – but it can’t insert items.
Rows can be deleted, hidden, and un-hidden. If you do the latter two, then you’ll want to set vertical spacing (of the hideable item) to None. Hiding an item does not hide its spacing.