Looks like GoldenraintreeÃ¢â‚¬â€Koelreuteria paniculata, to me. They reseed so much that it would be something that would be common to find popping up hear and there.
I noticed that you may be in Brazil, and if that is true I would consider NOT planting this tree as it is very invasive. Zone-wise it may not do well, either, although I know very little about your location.
Double-check with my answer and see if it is the Koelreuteria, but if it is, like I said, it can get away from you easily. I would hate to see your native plants take a beating.