Here are some rough sketches I started when this idea broke into my mind.

This one shows a sky view of what I'm wanting, the red is the main floorspace.
The arrow indicates that the distance from the wall that sits on the tree to the wall that faces outside is 6 feet. I figured that was good seeing as its my arm-span. I'm wanting it to extend 9 feet around the tree (also the red area)


This one shows what I am wanting it to look like from the outside. (Working from roof to ground)
I want the roof to be angled by about 40* to keep from rain or snow collapsing it in.
The main walls I was either going to make only two feet up and the last 5 feet being walls that can move up so that sunlight can come in. Or just make plain walls and cut windows into them. Like I said 7 feet tall to allow even taller people in.
And two sections of floor supporting beams; a short inner section that will connect to the tree and a outer longer section that will extend to the ground.

Ok tree apartment is more likely for what i'm wanting, thank you everyone who is helping with guiding me or imputing ideas,if I havent mentioned already the tree goes to about 15 feet before the big branches start

Wow, And Ambitous. I guess I didn't read the original post well enough either. Framing that is going to be be a major project. You could use framing brackets (Hurricane clips) against the tree using 3" decking or drywall screws. They allow you a good t0olerance for angle errors as well. The parameter joists top and bottom? Laminated plywood and perfectly round or alot of mitered joints. I would attach runners underneath the deck to 4x4'* to grouns either way. The umbrella type support to tree will putting alot of stress on something that can be taken down by snow and a hard wind before you add the weight of all the weight of the structure to it. It'* easy to lose sight of weight in a project like this. It would surprise you if you stacked it all on a scale before you erected it. Not only do you have the weight of what you want to put on.in the structure, you have that to add dealing with bottom support. Where will the stairs figure into this?

In the first picture, along the two flat angles will be the door and stair down from there. Because of all the weight is why I figured two sections of lower support, one fixed to the tree and one fixed to the ground, and I haven't figured in any upper support yet. The second picture, that is the roof, I'm not very good at making it look like an angled section. In the first picture, its very slight but on the outside there are 7 circles that indicate where the floor to ground beams are going to be. In between those 7 beams I will put 6 more beans that extent to the tree and will be fixed into the tree somehow.

Going 360 degrees with angles is even harder to cut join than draw. Takes a patient old Amish framer. LOL

If you use the "clips" I spoke of, no other support would be needed on the roof on the inside. They have 3 holes on each side of the bracket for screws. 4 inchers should take the stress considering all the brackets that will be in place. Using a screw that long is easier is a tiny pilot hole is drilled first.

I took your rough drawing and played with it. If you framed runners under the floor joists as shown and sunk the 4x4'* as I suggested, they will take alot more weight than your putting on them. A good deal of load will be on the tree. It'* not centered or in scale but gives you an idea.

So the yellow are the 4x4'* going into the ground and the black are the 2x4'* under the floors? Would I use the clips to put the floorborads into the tree?

Yes, yes, and yes. They have them at Lowes or Home Depot and make easy work out of harder projects. I use them for everything here. Nothing holds like them, and when your working alone it makes things alot easier. To really make the inner roof secure even further you can cut blocks of wood to fit between the clips and nail to tree. Here'* a animated pic of a Joist clip. They come in several styles, this one is my fav. They also come for 2 X 4, 6, 8 inch boards.

Ok, so This is going to use alot less wood than what I originally anticipated

. It will look alot cleaner as well. Looking the sketch of yours I altered over, remember it'* was just a rough revisement to give you an idea. You would want those runners beyond the halfway mark distance between the tree and the outer parameter. Given the length you suggest, not by much though. Another suggestion, why go 6 when 8 is the length of the boards you have to buy? Why not 7 1/2 and leave yourself some wiggle room for variances in the tree trunk.

I figured I could buy 12' boards and only have to buy half the amount of boards. But I might buy the 8'instead.