If you have clay soil, or soil that drains slowly after rain, save your back and don’t dig into it to plant your tree.
Loosen up the surface, spread some gypsum and mound up some good garden soil and plant into that. This will give your tree good drainage.
By the time it’s roots get down to the original soil level, the gypsum, worms and organic matter will have done their job and loosened up the soil enough to allow the roots to draw nutrients from the clay.
If your soil is more open or even sandy then the addition of some organic matter will help to give your tree a good start. The compost should be VERY WELL DECOMPOSED before you use it near your plants. A compost such as Kriedemanns organic compost or composted cow manure can be mixed with the existing soil to plant your tree.