This tree is bearing cherry-size fruit, but I know they aren't cherries. I think they are immature plums, from the look of the tree. Any sure ID from you folks? Leaves finely serrated and dark burgundy / green, fruit round like dark cherry, but no indentation where they attach to the stem. See picture...
Purpleleaf plum. Many commercially circulated, named selections as well as self-sown or casually planted unnamed seedlings. Very common.