Indeed this a most fine, small, native tree. It is Groundsel-tree (Baccharis halimifolia) in the Aster Tribe (Astereae) of the Daisy Family (Asteraceae). it occurs along the eastern seaboard of North America, from Nova Scotia to Mexico, and also on the Isle of Cuba.
Groundsel-tree flowers in the Fall with male and female flowers on separate plants (dioecy). It looks like your tree produces female flowers. That will be nice, as the feathy pappus on the seeds also makes an attractive display.
There are many species of Baccharis that occur through out the American continents. In California, I have several Coyote Bush (Baccharis pilularis) in my Garden, all of which self-sowed from wild seed. It is similar to B. halimifolia, but rthe leaves are toothed and it doesn't get quite as large, though my largest shrub is ten feet tall and beginning to resemble a small tree.