songsparrow.com sells tps in containers; their planting instructions say: "The tree peony should be planted so that the top of the soil ball is at ground level." Planting an inch or two lower than this might be a good idea, to encourage the plant to go own root.

I prefer to plant them about four inches deeper than they were in the container. Most tree peonies are grafted on herbaceous peony roots and by planting deep you will usually prevent shoots from the rootstock growing and competing with the tree peony. Roots may also grow from the tree peony stem from adventitious buds and add more nutrients to the tree. Al

Thank you both - I will plant it deeper then the soil level.