Redditor ArborCasa was hired to build this tree house. Here he details his process. In the end he builds a tree house the whole neighbourhood will be envious over.

via ArborCasa

The Tree
The tree chosen was a live oak with three main branches.

The Property
The land is situated on a hillside. There was an existing deck attached to the house (far right) across from the tree (branches on the far left), with a gravel road in between. Because of the tree being on the hillside, and the height of the house, he opted not to use a rope ladder, but rather build a bridge that runs across the road.

Beginning of Bridge Building
Concrete was poured to create a foundation 4 feet deep and 1 foot wide, and post anchors were set into the wet concrete. The framework is made out of 4″x6″ pressure treated Douglas fir, brackets, and lag screws.

Bridge Framing On Tree House Side
The height difference is apparent.

Bridge Complete!

Side View Of Bridge
Disassembled wine barrels were used as balusters.

A View From Underneath

Side View Of Bridge Extending To The Tree
Two 4″x10″x24′ pressure treated beams had to be special ordered. The bridge is tall enough for vehicles to pass underneath.

Floor Beams Going In
When attaching the wood to the tree, it must be taken into account that the tree will sway with the wind. To circumvent damage to house caused by the movement of the tree, sliding beam brackets were made, with custom-made 1″x12″ grade 8 screws to fasten into the tree.

Decking Boards Attached

Deck Complete

A View From Underneath

Framing Starts
The house itself is 8 feet wide by 12 feet long, with a two foot walkway around the tree house.

Side View

Framing Finished And Ready For Sheathing

Waterproofing And Windows Installed

Trim Installed, Cedar Siding Installation Commences

Cedar Siding Complete

Interior
The finish material is pine shiplap planks. The tree house is equipped with electricity, water, phone, cable, and internet, with in-wall speaker wiring.

More Interior

The Completed Product!

Side View

View From The Rear Window