A lot of trees will have roots across the top of the soil...
Why do you care? :-) It's not hurting the trees.

If you are concerned about looks and tripping over them, just bring
in a truckload of good soil and re-bury them. Build a circular rock
border to hold the dirt and plant a shade garden.

That's what I'd do anyway?

If you bury the roots very deep, you'll kill the tree. Someone who knows
please chime in, but I believe you shouldn't add more than one or two inches
of soil.