These are known as “mulch volcanoes”. They are terrible for trees and this should be avoided. If you’re planting a new tree, don’t do this and if you have an existing tree like this, pull away the excessive mulch and soil. A slight depression in the opposite direction, like a shallow saucer, allows for water retention as a tree is getting established. (Some people refer to this as a “doughnut.”) You should be able to see the part of the tree that “flares” out.Mulch is fine under a tree, but not