I took a few pictures of trees to get an idea of how they look, and some elements of branches and whatnot that I thought would work. I did my best to draw some sketches, but I'm not particularly adept at it and I didn't like what came of it. I got together with two friends: Antoni, a sculptor, and Brandon, an architect to talk about the project. Overall it wasn't too productive, but at least it was a start.
One thing I think is important is to have a spiral ramp—not stairs or ladders—to access the main level. I don't understand why it needs to be a spiral, but it needs to be a ramp to permit people with limited mobility to access it.
It also needs an interior space—a sanctuary for ceremonies and reflection. The yurt provides this. It also helps the stability, since a real tree of such size would have a substantial root structure to anchor it; an artificially-wide trunk would mitigate the instability in absence of such a root structure.
Toni encouraged me to start making models using toothpicks as, say, 8' framing members and see what I could come up with. He suggested we make a 1/6 scale model (e.g. "Barbie size") and burn it, say, on the Solstice: December 21.