Asolutely no mulch volcanoes around trees and shrubs unless you own a
Wal-Mart parking lot and then it is expected.
Most all roots are in the top foot of soil, that's where the air for
respiration is.
Take a spade and turn the blade so you pierce the soil in line with the
shrub as if the shrub was the hub of a wheel and the spade was making
the spokes. Pry the spade back and forth a bit and drop some compost in
the slots. Topdress with an inch or so of sifted compost or shredded
leaves. Keep adding them as they decay and disappear as organic
material does get consumed.