Here’s the Bridged Treehouse. This is a CC Free lot, so I urge you to redecorate ;)
This one is a little more spacious, with 1 bedroom, 1.5 bathrooms, and a 3rd deck area for entertaining. There is plenty of room to add a garden. Also, the mailbox is in the tree trunk, just ‘cause ;), but its been tested and works.
I have tested this lot, but if you have any problems please let me know! I have all EPs, and have used items from most of them, but if you’re missing an EP I believe the objects will just be replaced. However, you’re at least going to want Generations for the spiral stairs, and World Adventures for the tree.
One thing about tree houses in TS3 is that you’re gonna have branches all over the inside of your house. So don’t freak out when you first open up the lot and see.. well, a tree in your house. Once you zoom in it will disappear :)