Fertilizing trees is a different process
In forests, trees shade out grass and other plants so the tree’s roots don’t have to compete with roots of other plants. Trees are free to absorb all the nutrients they need. Your lawn is a harsher environment for trees. In your lawn, trees must compete with grass roots for valuable nutrients. When you drop fertilizer on top of your lawn, the grass receives most of the benefits.
A different type and method of fertilization is used to fertilize trees than what is used to fertilize lawns, since trees don’t grow the same as grass. For trees, slow release fertilizer is applied directly to the tree roots, just below the grass roots. This can be done with special liquid fertilizers injected into the soil (sometimes called “deep-root fertilization”) or dry fertilizers poured into the ground.