It's not a tree I've ever seen in person but maybe Melia azedarach, Chinaberry?

I thought it was one of the trees from the Arbor Day Foundation, but they would never send a chinaberry.
If so, then the seeds must have sprouted in an empty pot.

It could be a Koelruetaria elegans.

Koelreuteria has opposite leaflets. And now I check more carefully so does Melia azedarach. The OP's tree has alternate. Does the ADF publish a list of species it sends out?

Here's their list ("All Trees" -- a dozen at a time):
http://shop.arborday.org/category.aspx?zcid=130

Maybe i'm confused....

Here is a link that might be useful: {{gwi:318953}}

Koelreuteria has opposite leaflets. And now I check more carefully so does Melia azedarach. The OP's tree has alternate.

From the pictures I see, the tree has alternate LEAVES but opposite LEAFLET arrangement.

Aswhad - you're right. I looked at Koelreuteria elegans and it appeared to have opposite leaflets but in your picture I see that that is just a function of the angle. Some are discernible as alternate. I had another look at the OP's picture and to me the leafLETS still appear alternate. If you go back one image from the first which appears there's a close up of the leaflet arrangement. So Koelreuteria is still a possibility while Melia isn't. I've only seen K paniculata, so can't comment on K elegans. From a quick look it doesn't seem to be in the ADF calalogue.

Now I've confused myself ;-)

The leaves are definitely alternate, while the leaflets are opposite, as are the blades. I am leaning toward goldenrain tree so far.

Maybe we are at cross purposes as to what we mean by leaf and leaflet? The smallest unit I am calling a leaflet. These are alternate in the photos. They go to make up opposite pinnate leaves. These in turn make up alternate bipinnate leaves.

Thanks, all of you, for helping to ID this tree.

floral_uk, I see what you're saying.