Hello,

That looks like a gall, or growth caused by a fungal canker (as opposed to a bacterial canker, which usually causes affected areas to appear sunken). Black knot commonly causes fungal cankers; are there black growths on the branches, too?

https://extension.umn.edu/plant-diseases/black-knot#using-fungicides-1170312

The article at the link describes treatment for branch cankers; best treatment is to cut them out. However, because this is a trunk canker, it might be more difficult to treat. In fact, I would recommend contacting a certified arborist for assistance in this case. A certified arborist visit will likely have a fee associated with it, and can result in saving the tree. Arborists are certified through the International Society of Arboriculture (ISA) and they maintain a website that makes it easy to find a certified arborist. 

https://www.treesaregood.org/findanarborist/findanarborist

If you have any questions about the information provided, please feel free to reach out. 

Thank you,

Julie