Melilotus?

Trifolium hybridum?

Not a tree. Maybe Alfalfa or one of the above suggestions. A member of the clover gang anyhow.

Yes, I thought lucerne (aka alfalfa).

Mybrownthumbz had it. Melilotus leaves are serrated along the entire leaf margin, and Medicago sativa,(alfalfa) leaves are serated only near the tip. White and yellow sweetclover are nearly impossible to tell apart, until they bloom, and the 2 types bloom weeks apart. Some botanists consider them both the same species, Melilotus officinalis, while others believe Melilotus albus is a unique species. BONAP treats them as one species, and has M. officinalis listed, (with yellow and white combined), but M. albus is not listed. These sweetclovers have strong, deep roots, and you need to dig all the roots out, or they will grow back. They were brought from Europe for grazing, and later for beekeepers. Acres of them were grown in every state.

Melilotus officinalis, the light blue is the counties where it has been recorded. This map is white, and yellow Melilotus combined, and treated as Melilotus officinalis. Trifolium hybridum has trifoliate leaves, with leaflets that are nearly sessile with no petiolules. The center leaflet of Melilotus has a long petiolule, while the 2 outer leaves have very short petiolules.