In most cases, no soil amendments are needed at the time of planting a fruit tree. Ultimately, for practical purposes, a fruit tree must grow in the native soil: either it will tolerate it or it won't. In any case, do not burn a new tree's tender feeder roots with fertilizer or uncomposted manure. Mulch or compost is best applied on the surface after planting, rather than mixed into the soil.
If planting a bareroot tree in very fast-draining sandy soil, however, mixing some well-composted organic matter in the planting hole will help retain water in the vicinity of the emerging feeder roots and help establish the tree. (If planting in slow-draining clay soil, elevate the planting with a berm or raised bed.)
If you are unsure about the benefits of soil amendments in your location and want to do a test, plant some trees with amendments and some of the same type of tree on the same rootstock without. Wait til the trees are established and you have observed them in both wet and dry conditions before judging results.
For more about planting fruit trees, see Planting Your Backyard Orchard.