Tree

When I was a kid, I had this notion— don't know how it came to me, but I think it may have been in a dream— that God had created the world, because God lay down beneath a tree and took a nap, and dreamed the entire world, and so decided to create everything in the dream.

Variant telling: God dreamed about a tree, and so decided to create an entire universe in which for there to be a tree.

Of course, in a mediaeval morality play, this would have been the tree on Golgotha.