Never add compost (Dead plant material) into the soil when you plant your tree. The dead plant material will decay, form a thick sludge, and cause damage to the expanding root system. Only add compost on top of the soil, just like mother nature, and feed the plant from the top by watering.
The only thing you should be adding to the soil when planting the tree is Pumice or washed sand if your soil is heavy. This will help break up the heavy soil and also improve drainage.
Johnny