How can you create a tagging widget via lua in Darktable?

I’m trying to create a widget that shows a specific set of hierarchical tags. Well, two widgets. On the left hand side of the lighttable view would be a widget for filtering your pictures. On the right hand side would be a widget for adding tags to the hierarchy. My focus right now is the left hand widget.

So far I haven’t been able to figure out which widget type will actually give me what I want. A box is just a wrapping around other widgets (right?), a combobox gives me a dropdown menu, entry and text_view are text entry inputs, and none of the other types seem to fit either. How can I get an expanded select list? And how can I make it display like a tree?

I’ve been using the lua scripts repo as a guide, but I haven’t found an example of what I need in it. At least not yet, I’m still going through them.

Feel free to point me at the right docs or an example plugin.

Thanks in advance!