Here's how I'd do it (and I have successfully transplanted several free trees).
First make sure the tree has been well watered a few days before you plan on moving it . Transplanting is stressful enough without also having a drought stressed tree. You don't want the soil drippy wet when you dig it, but nicely damp soil should hold a decent root ball.
You didn't mention how big it is or if it's leafed out already, it would be best of course if it were still dormant, but no biggie, it can still be done.
Have the hole you're putting into at home already dug, make sure it's plenty wide, ( you don't want to cramp the roots ) and fill it with water a few times to make sure there will be deep moisture available.
If you can find it in your area "Superthrive " is a good thing to have on hand to water the tree in with once you've transplanted it. (Ignore the hyperbole on the label, it's not a cure-all, but has been shown in gardener trials to help with growing new roots.)
Dig the tree with a wide root ball, probably a little further out than the dripline. The more roots you can keep the better. You will inevitably damage roots, and some will just have to be cut off, so don't lose any sleep over that, just do what's reasonable.
Bundle it up in trash bags, wet burlap, or whatever you can to keep those roots from drying.
Quickly get it home and into it's new hole. Don't use any soil amendments in the planting hole. That used to be recommended, but now it's been found to keep the roots from growing into the native soil. Backfill the hole about halfway, then run water into the hole to settle the roots and remove air pockets. Continue to backfill the hole until the tree is at the same level as it was in the old hole. You can tell by the marks on the trunk. You do not want to
plant it too deep. Make a watering basin a few inches high and water it in with the Superthrive.
It may wilt,and if it's blooming I would pick the blooms off so all the energy goes into root formation. You can mulch it with a few inches of compost, holding it back about 4 inches from the trunk. Then it's just a matter of keeping it watered, probably letting the surface of the soil dry out to about 2 inches deep between waterings. You won't get any fruit this year obviously, but hopefully it won't miss a beat,and you've got yourself a new tree with a little sweat equity!
Hope all that is helpful, let us know how it turns out!
My little Bonnie Best apple tree is going into it's second year since I planted it and it's about 5' tall now and 3' wide. I've never moved an older tree before, but I do know the roots will go out about as far as the branches reach outward. That's your dripline. You don't want to lose too many of those roots, so you'll probably be digging a pretty big hole. They go wider than they do deep.
