This is risky. Wood absorbs any liquid it comes into contact with, and deeply. It is impossible to get all of this out of the wood, and it can leech out over time. I certainly would never put wood that has been "treated" into a tank with fish.
And before it is mentioned, I understand that are those who will use hydrogen peroxide in a tank with fish, but this is irresponsible. All substances added to the water get inside the fish by normal processes, and this does affect fish no matter how "safe" some think it is.
Byron.