I have seen people suggest that it is angels (though that would mean God has spaceships) and that was the tree of life....then the other obvious one is it is simply aliens though one could expound on that and say that they are suggesting that angels are actually aliens. Lots of ways to go off on that ending. My normally non-sarcastic wife had a funny, sarcastic one liner with that tree scene when she said, "Time to eat some Apples."