Ash-Leaf Maple (Acer negundo). Ash-Leaf Maple, or Box Elder, is the only maple in North America with compound leaves. The dangling flowers appear in early spring just as the leaves are beginning to show themselves.
This tree tends to take over hedges in the city, and perhaps the best way to deal with that is just to let it take over. The leaves often have three leaflets, making them easy to mistake for Poison Ivy.