Raising soil level around a trees root flare is detrimentally identical to planting too deeply. Humans assumed trees produced Oxygen as a byproduct, but actually its an essential ingredient utilized by their root system just below ground. When these roots get smothered by Mulch or added soil, they act like drowning swimmers and immediately come up for air above obstruction. And just like disoriented swimmers, many times these rising roots end up growing toward trunk instead of radially away. If walled in like topics example, rather than dive below obstruction to get past it, roots will take easiest route and stay near oxygen supply while inevitably circling around trunk.
All combined, these detrimental effects will rot out soil moist trunk defenseless to insects and disease, along with producing "Girdling roots" which will inevitably strangle trees stem. Causing portions of crown to die off, or worse becoming public safety issue after constricted trunk snaps off from its base! Make sure tree is installed at "Root flare" level or two inches higher. Are you "Killing your tree's beautifully"? I suggest watching "This old house tree mulching" video on YouTube to become more educated about subject!