If ownership means that no one else is excluding you from using that tree, then you're right.
But I think ownership means more than that. It also means that you have a right to exclude others from it. Once you turn it into a chair, it is your right to do that. But until you begin doing that, if somebody else turns it into a chair, then it's their chair. You don't have a right to just point to the tree whose existence owes nothing to your labor and declare it yours until you eventually get around to doing something with it. Similarly, you don't have a right to draw a big square on the ground and declare that you own everything inside it, along with the right to exclude others from it and everything below and above it, without you laboring there while you simultaneously demand that others can't labor there either.