The list in post #9 above may be reasonably reliable. I am only saying that because some of what is listed especially the "do not use" species is accurate, those are highly toxic. I do know from discussions with biologists that oak and beech are safe as far as the wood itself, and the dried leaves of these trees. Maple leaves were deemed safe on some sites I came across a while back, so I would assume the wood is too, but this is just my assumption.
Having said that, you are always safer to purchase wood from a reliable fish store. I know, it is expensive, but it should (note, I say "should") be safe. Malaysian Driftwood is what I have been using for years. The other types especially the branching wood is risky for toxic fungi.
The other thing about collecting wood like oak and beech is that it must be completely dead dry, which means the wood must have become separated from the growing tree years ago so it can completely dry out. Then there is the issue of waterlogging so it will remain down in the tank and not float for months depending upon the size. And another issue is the collecting site; wood will readily absorb any liquid it comes into contact with, and there is no method to get these out quickly; they can leech out for months and even years, and in an aquarium this can be deadly due to the closed space.
I use dried leaves from oak and maple, collected from my rear garden where I know there are no chemicals, pesticides, fertilizers, etc. I use small branches that the squirrels break off from the oak tree, after they have been on the ground for several months, and even then I leave them in a dry room for months before use. I would never risk larger or thicker chunks of wood.