When I was flipping bikes I took a couple of very high end biked in that had front end crash damage. I was able to straightened two out of three so they looked correct and measured very close.. I did not think of the tree method but i did use a strong pipe thought the headtube and bolted it to my heavy outside workbench and jacked the frame straight. The hardest was making a clamp for the jack head to mount against the BB. I pretty much copied the Campy frame straightening tool.
Ed