Answer: The general rule of thumb is to leave the exposed tree roots alone and not cover them with soil. Depending upon the tree, extra soil could damage the roots, cause rot if it holds too much moisture against the bark of the roots, and exclude air which could suffocate the roots. I've found that you can grow groundcover beneath a tree which will gradually grow over the exposed roots and hide them from view without compromising the health of the tree. Exposed roots are just part of the character of the tree within the landscape so I'd be inclined to just leave them alone. Best wishes with your landscape.
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