Growing near the tree the plant would need to tolerate at least partial shade, especially as the tree grows in size. Heucheras might be a good choice. They can take full sun or part shade. Many are grown more for their colorful foliage than their flowers, so they're attractive all season long. Platycodon (balloon flower) would also work in this situation. Pulmonaria (Bethlehem sage) might be another good choice.