I would like to know how best to look after a plum tree that has a second trunk. No fruit for two years. How do I fix this tree?
What to Do With a Plum Tree That Has a Second Trunk?
Certified GKH Gardening Expert
Did a 2nd branch or trunk grow from below the graft on the tree?
If this is the case, it is likely that that branch is taking energy from the tree.
You could prune the tree to one main tree, make sure you remove the one that is from below the graft.
Pruning should be done in early spring.
Here is a few links with more information.