Did it start out as 4 separate trees and they were just somehow manipulated so that they grew together? This is amazing, and completely bizarre, all at the same time!!!
http://inhabitat.com/interview-becky-northey-and-peter-pook-cook-on-the-tree-shaping-art-of-pooktre/ This guy makes all sorts of living furniture. 4 trees and a lot of time and patience.