It is a nursery tree digger. I know several people that have them here in Wa State and have seen them in operation. They straddle the nursery tree that has been grown for one season (here it is apple, pear or cherry). Then there is an under cutter that cuts through any roots and pulls the tree up. Then some times there is a sort of beater to knock loose soil off.
The fanciest one I have seen is actually pulled by a 200hp wheel tractor at Willow Drive Nursery in Ephrata, Wa. I wish I would have taken a video. There gizmo dug trees on the right and then used gripping belts to pluck it from the ground, and a series of beaters knocked dirt from the roots as it traveled to the left side of the tractor. There it was tossed into the waiting hands of someone to load the trees onto a wagon. They have three diggers and dig something like a million trees in a week.
Come to think of it, I think we to be in partners with someone on one about 25-30 years ago. I wasn't very old then.