I want ground support but don’t want to damage roots

I have a conundrum (to me at least). I want to build a simple (posts and a platform with rails around the side) “treehouse” between 7 and 10 feet tall beside a large bitternut hickory, and I want it to be ground supported.

I see that ground supported treehouses have posts on concrete that was poured into deep holes. I don’t feel comfortable digging into the ground right beside the tree because the roots are huge, near the surface, and I’m afraid I will kill my tree.

Is there anyone here who can give advice and help me think through this?