[greymule]

From what you describe, the high tree branches actually overhung the field. If they didn't and were behind the fence, it's a no-brainer. In your case, I'd consider the tree branches similar to an upper deck that overhangs the field. I think left field in the Polo Grounds overhung a little. Home run.

Since the ball was apparently on its way far over the fence, you shouldn't get too much argument. But what if it was a high fly that hit a branch with the fielder camped under it? Good thing to cover in the ground rules next time.