what's the least painful way to transplant a tree?

do it while it's dormant - autumn after the leaves drop or early spring before buds open. water it well the day before, then dig as wide a root ball as you can physically lift, and keep as much soil on the roots as possible. replant at exactly the same depth it was growing at, water deeply, and keep watering through its first summer, that's when moved trees die. realistically this is only easy for young ones, anything bigger than a few inches across the trunk is a pro job.