why does my black mulberry tree with fruit have knots on it\'s trunk
Certified GKH Gardening Expert
These tree trunk infections called "burls" look like bumps or warty growths probably caused as a result of environmental injury. Cambial growth is hyper-stimulated as a way for the tree to isolate and contain the injury. Almost all burl wood is covered by bark, even when underground.
You may want to have the tree inspected by a Arborist.