Any particulate piece of wood you want to use?
From my experience, I'd rather pay for a treated piece, less problems later on. Starting out with the "right" piece of wood might help, most pieces I have attempted to treat and use are still releasing tannis into the water and some pieces have become soft where I had to remove them from the aquarium before they start to rot. On the positive side, I have a pleco that loves feasting on the outer soft layers of the wood.
There is plenty of good read on this topic on the net where you might find most the answers you are looking for.