I have done this several times and have a 30 foot tree in my garden that originally came from Italy. With propogating we have grown at least 25 other trees mostly given away to other over about 20 years. They give excellent fruit.
Here is how you do it. Pick a well established branch that already looks like a tree and has a few branches off it. It should have a faily robust and straight main branch. Look for a branch that you can plant as a good start to a tree. This should be about 4 foot big, much bigger if possible. Cut a groove into this branch where the tree will start. This is where the root will come from. You need to surround this with rooting compost, and water it for at least 6 months.
Get a two litre plastic lemonaid bottle or equivelent. cut off the top third. Next split it right down to the bottom of the bottle, and to the centre of the bottom of the bottle. Then cut a little hole at the centre of the bottom of the bottle where the split ends so that the branch can fit through it, and the bottle wraps back around the branch forming the bottle shape again. The tube that is made from the bottle shape is filled with rooting compost taped back shut. The open end is pointing up your new tree, so the water and soil stays in. Water well for the duration while the roots grow big and strong. You need to do this until the roots are visable and fill a great deal of the plastic bottle. Only then do you cut down the branch at the base of the bottle to replant and start a new tree. Put into a prepared hole in good soild with plenty of compost lining it. Water it well for a few months. Hope you have success. x