Your tree is a fairly old tree with some poor branching. It looks like you have a fungus growing which could indicate that it has been infected and is decaying. Here is a link that explains wood decay. http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/wood-decay/ . I would have a certified arborist come and take a look at your tree. They can tell you what it is for sure and if there is anything that can be done. It may be possible to prune it but I don't know if that will help or not. Here is a link to help you find a certified arborist. http://www.treesaregood.org/findanarborist/arboristsearch.aspx