You can, and it's an organic material. Like you said, don't use pressure-treated (or any kind of treated) lumber--if I remember arights, the arsenic levels are pretty high.

I'm not sure about the glue. It's probably a plastic or rubber-like thing, so it won't decay.

Now a warning. :-) Wood is a "brown" and very high in carbon. It's going to suck up nitrogen to decay (and then release it as the decay process continues). You'll want to counterbalance that with a nitrogen source.