So a day after I posted photos of the mystery plant. I just got a few responses:
– Schinus terebinthifolius, which I still don’t think it is because it doesn’t quite match this photo.
– Kentucky Coffeetree, Gymnocladus dioicus, which I don’t think it is.

So I did more research using the Virginia Tech VTree ID Leaf Key website. After all the questions, this is what I came down to this page:
leafy, broad leaves > alternate leaf arrangement > compound leaf > pinnately compound > singly pinnate > serrate, toothed, or spine-tipped leaflet edges

I found two photos that reminds me of our mystery plant. One is a Smooth Sumac (Rhus glabra) and the other is a European Mountain Ash (Sorbus aucuparia).

The search continues…