Here is an example of a Mulberry (red) branch that is growing sideways to get light. I thought the tree was over topped and had sent this lateral to acquire light. As I backed up to see what was overtopping the tree there was nothing above it. So it is a riddle. There may have been a tree there that had died in the past.
Maybe the tree has recently gained dominance in the forest and sent out this branch before that happened.