Maackia amurensis ?

Perhaps the Japanese pagoda tree (Styphnolobium japonicum) which is hardy for your zone? You could compare it and see what you think.

FataMorgana

Hmm, the flowers look like a decent fit to maackia (but not styphnolobium). Leaves are a good match too. But the flowering time for maackia is supposed to be June, not late summer. Perhaps it's confused?

The late bloom time was one of the reasons I suggested a Styphnolobium. Here are pictures I took last year of a Styphnolobium japonicum blooming at the very end of August here in Western NY State. It had fat seed pods a month later. You can compare the images with your tree and see what you think.

FataMorgana

Trunk

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Flowers

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Leaves

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Tree

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Seed Pods

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