One of my favorite times of the year
When I first moved into my house, it was November, so I had no idea what the trees where. I figured they were some kind of fruit tree, but was sorely disappointed when spring arrived and everyone else's trees were in full bloom and mine were... not. At all. Then, spring progressed, and toward the end of May, beginning of June...*boom!* sweet-smelling cloudy goodness. I love them!
I think my fringe trees are Chionanthus virginicus
, a native plant, hardy in zone 3-9. It produces small dark fruit that's not consumable by humans... but the birds love them. They do have to be planted in male/female pairs to produce fruit, though.
There is a Chinese version Chionanthus retusus
. It tends to be smaller than the native tree (though the native is slow growing and not very tall either), and blooms in early spring, rather than late (they say).
Though, I'm not exactly sure how you tell them apart! Of the photos of the flowers of both that I have found, my trees looks like the native.
EDIT: I found out one that one of the major differentiators between the native and Chinese versions: C. retusus has upright flower panicles, and C. virginicus has semi-pendant to pendant flower panicles. You can really see the difference when you compare The Chinese fringe tree flowers to the ones I posted.
Mine are pendant, and cluster under the leaves.