I bought a yard of fabric, but I have a tall and skinny tree. You could do this with more if you had a larger tree.
Then I folded it into a square, and used a pencil as a compass with a piece of leftover fabric.
Then I cut up one slit and cut a small circle out. (I wish I would have gone even smaller!)
Next I folded over the cut and center circle and made a nice edge.
I sewed that all the way around!