Swiss Family Robinson Treehouse

This tree is super solid. Can you guess how I built it this way? My first attempt took about three weeks and then totally fell apart. Three months later I had a solid build. I made two different sizes. One super big and the other large. The smaller one is up on Lego ideas so please go VOTE for it there. Here is the link: ideas.lego.com/projects/e299db50-89bc-41e5-a69d-1f51520093e4

Done