If you want to start a tree from a cutting, look up "air layering". Some kinds of trees can be started from green or dormant cuttings and others can't. The problem is that when you try to start a tree from a cutting, the cutting has to produce sufficient roots quickly enough to support the top. Air layering, keeps the cutting attached to and fed by the tree while roots are being produced. You can generally get better success rates with this. One trick I've seen is to constrict the branch with a wire for a time period prior to air layering. This causes auxin to build facilitating root production.
Keep in mind that if you do this with an apple or pear tree, you will get a full size tree. This may or may not what you want. Full size trees take quite a while to bear fruit. What advantage do you see of using a cutting verses buying root stock for $2 or $3 bucks and grafting the scion to it?
Thanks,
Jack