Depends upon why it's not fruiting. For instance, if green, vigorous and growing rapidly, could be excess nitrogen. Or if pale, nearly leafless, with numerous dead branches, could be be short of water. Or too little sunlight.

Is it indoors or out? In a pot or the ground?

Post an image or two, please, of the entire tree, also a midway shot.

Oh yes, and where are you?

Another problem could be the grafted part of the tree died off and the root stock took over. In that case you would need to re-graft the tree.