The pot you have it is is probably already too deep with soil. The nurseries usually add more dirt as they move them from small pots to the larger ones the eventually sell them in.
When you are ready to plant the tree, have some compost tea and a large bucket or bin and mix water and compost tea then soak the tree roots for a while (maybe an hour, depending on the size of the pot) and loosen the dirt and any roots that are wrapped around. Carefully pull the dirt off the top of the root and look at the trunk - you need to have not only the graft exposed but the beginning of the flare visible. The hole you dig should be shallow enough that the tree flare should be level or a little above the surrounding soil when you fill the dirt back in around it.
Read this: Planting Trees Errors
for a more thorough description.