I had several tree houses as a kid. One built on top of two telephone poles, another in a large old tree. One morning I got up in the tree house to find it had been "Initiated" by some local college kids. Cigars butts and condoms said:"Hi little boy! The big kids were here last night."
The tree house was quite a distance from my Parent's house and no close neighbors near the tree house either. (Which made setting up a scare one night easier)
Very cool. One of friends dad built us one once that was two story. It had a ladder that went up a side of a fence to the second story and there was a trap door to also go up. It was wonderful. Such great memories of it.