Answer:
Look into my face and I'm everybody. Scratch my back and I'm nobody.
Face with a tree, skin like the sea. A great beast I am. Yet vermin frightens me.
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
What has roots that nobody sees, and is taller than trees. Up, up it goes, and yet it never grows.
White fat and fluffy, May even look like a puppy. Seems heavy but is light, Floats about without a worry, But if it turns dark you have to hurry!
What covers its face with its hands, speaks no language, yet most known what it's saying?