"Money Tree Seeds" are a popular gift...and a joke/gag gift. The seeds can be from any type of fast-growing plant.
There is another plant called a "Money Tree Plant' - Pachira aquatica aka Bombax glabrum, but the seeds look (to me) more like a striped snail shell and are not flat as you described yours to be.
Please keep taking photos so we can watch your Money Tree as it grows.
