don't draw straight lines. When is anything in the world straight? I'm not sure if you are wearing monks robes, a crafting apron, or a potato sack, so you should work on that. It is a little bit unrealistic because unless you cut the tree down then ran to the otherside while it was falling it doesn't make sense. Just pay attention to details. Look at it, make some changes, come back later, make some more changes. A good sig is edited many many many times.