I’d remove the rocks around the tree. If possible, work on the lawn or convert to ground cover.
There are SO many shade-loving options. Don’t know where you live specifically, but Herring Run Nursery is a great place to get native plants (they’re in Baltimore) as is The Perennial Farm (the scope of it will blow your mind). If you live further north, Schott Nursery is a wholesale nursery that sells retail on Saturday only and their prices are FABULOUS.
Some plants I sorely miss from my shade garden (they do well in part shade as well); spiderwort, clethra, Virginia bluebells, lady’s mantle, white wood aster, heuchera, wild geranium, blue wood phlox. I know I’m forgetting some. I also decided to list the common name instead of the Latin to make it more “newbie” friendly.
Q