I've got this volunteer tree/shrub coming up in my backyard, and I'm having trouble identifying it. I think it's some sort of cherry, but it's shaped like a birch tree and it's growing incredibly fast. All of this is last year's growth, so I'm flumoxed.

http://yardenthusiasts.com/photos/brotherjoe/images/179/original.aspx

Based on the leaf and fruit, I would lean towards cherry (Prunus) rather than birch. Couple follow up questions to narrow this down, what part of the country is this? What does the bark look like?