This is a fairly straight forward project with Crabapple trees brought together and grafted and then separated to form a frame slightly tilted away from the original plain. Due to the characteristics of this variety of crabapple tree, it is full grown at this point without much further growth potential to complete the frame at the top.
This extremely controlled upright frame project is two Elm trees. It is rigorously supported and held in position with a heavy wood armature and bolts because Elm doesn't hold a form until a few years have past and substantial hard wood has formed.
As a tree material, Elm does grow relatively quickly.