Since the image Jo Askerne posted as the OP here is now a broken image, I have inserted a generic treehouse to establish the OP of this thread. -- Ken Anderson
Tree houses don't last long enough. The tree usually grows out of it. Not worth stressing the tree. I didn't have a tree house. But I had a tree, with a series of about 4 limbs flat in row that you could lay down on safely and comfortably and read comic books. It eventually got too small. I didn't know trees shrunk also.
My husband and I came 'this close' to buying a house for its treehouse! until we realized we liked the treehouse better than the actual house!
Growing up with all boys except 2 much younger girl cousins we had several treehouses as kids, and even a few hands dug tunnels, in which one almost gave one of my cousins and I a premature burial when it caved in on us. Tree house fell to the ground just when my girl cousin was finally braving the climb and the limb broke, tree house landed on top of her.
We didn't have a tree house, but we did have a big tree that we spent a lot of time climbing. As a kid, I decided to make a "hammock" up in the tree from an old quilt and a bunch of big safety pins. Needless to say, it didn't work and I plummeted from what I thought was a terrifying height (but was probably not more than ten feet), knocked the wind out of myself and lay there thinking I was going to die before I got my breath back. Remember doing that? You just couldn't breathe for what seemed like a long, long time but was only a matter of seconds usually.
I never had a hand in building a treehouse, but we did have one in a large oak tree behind our house that one of my older brothers must have built, and my cousins and I spent a few nights there. Although there was a small apple orchard between the treehouse and the road, until the county cut the trees back, an area of the road just before our driveway had a tree canopy covering it. One day, my cousin Calvin and I strung about a dozen water balloons from the treehouse to the branches that covered the road, with the balloons hanging over the branches above the road and the other ends of the strings attaching them secured to some bent nails that we put into the wall of the treehouse. When a couple of our female cousins, Calvin's sister and another cousin who was in my grade came walking along the road, we unleashed the water bombs, one after another, and they couldn't even see where it was coming from. We estimated that at least half of them hit the targets.
There are businesses making "treehouses" that look more like elevated A-Frames, except these are nicer than A Frames. This one was made for an 11 year old girl who won a contest. I have no idea the longevity of these things regarding tree growth.