Why does this odd bicycle go up and down?

Most bicycles are designed to be ridden horizontally. So it was a bit odd to see the one designed by Ethan Schlussler that goes vertically. That's right, it goes up and down. But it definitely serves a practical purpose. CNN reports the hilarious and clever use of a bike by Schlussler:

Schlussler said he built the tree house nearly 30 feet up and "I got tired of climbing a ladder 6 1/2 million times a day, so I made a bicycle-powered elevator to solve this problem."

One of the CNN anchors mentioned seeing "a fault," saying once you're at the top, there isn't a way to get into the tree house.

To which Schlussler answered in comments below the YouTube post: "It’s not an engineering problem with the elevator or the tree house; I have simply not finished building the tree house yet. Even so, it is not a problem to climb over or under the railing…"

Perfect.