Two schools of thought exist on how deep to plant. One school wants the “top” of the root/dirt plug to be a tad above the new ground level. My school likes the plug top a tad below ground level. We then hand form a dirt berm around the tree just outside the hole rim so water can collect in the slight depression this forms. I like to move extra leaves, grass or duff in under the tree inside that berm as mulch to retard evaporation. Let me know how each works for you.
You can buy much larger trees, from one foot to several feet tall, that have been grown in their own pots, tubs or even in the ground and have then been “balled and burlapped”. After the Ham Lake Fire several cabin owners bought and planted a few larger trees around their cabin sites just so there would be something tall and green nearby. Potted trees can be stored for a while outside in the sun if kept watered, but as always plant them as soon as possible. Dig a hole slightly bigger than the pot is wide and tall, with a level bottom so no air pocket develops under the roots. Some folks add peat moss and bone meal underneath to loosen the soil the roots must penetrate and help feed the tree as it takes root in the new site. Roll the pot on its side and push lightly down while rolling to loosen the dirt inside. Slide the “plug” of dirt and roots out sideways and lift the plug into the hole, trying valiantly NOT to lift or move the tree by the trunk. Fill in the sides of the hole, packing firmly to avoid air pockets.