It's important not to plant the root collar of a tree below the surface of the soil. With balled and burlapped and containerized plants, proper planting depth should be determined after removing excess soil from the trunk to expose the root collar.
The diagram below can help you determine the proper depth for planting.
How to Plant a Tree
Keep the tree’s roots moist until the tree is planted. The hole should be as deep as the longest root and twice as wide as the root cluster. Create a small mound of soil at the base of the hole, place the roots on the mound, and gently add soil back into the hole, avoiding air pockets and compacted soil. Water the tree after planting.
Balled and Burlapped (B&B) Trees
Dig a hole twice the width and equal in depth to the root ball. Remove any wires, and place the tree in the middle of the hole. Remove any burlap without disturbing the root ball. Stabilize the tree with back fill. Add the rest of the soil back in the hole, avoiding air pockets and soil compaction. Water the tree after planting. This new video from Friends of Trees shows how to plant a B&B tree properly--and how to have fun as you plant it.
Remove the container from the tree, and dig down to find the top root or root flair. Dig a hole as deep as the distance from the top root to the bottom of the root ball and twice as wide. Gently tickle the roots to loosen them from the soil. If any roots are circling, slice the circling roots with a knife. Place the tree root ball gently in the hole by holding the root ball. Back fill. Avoid air pockets and soil compaction. Water the tree after planting. This video from TreeUtah shows how to plant a containerized tree properly.