Did it start out with more than one trunk or was a sucker allowed to grow into a trunk?  You need a certified arborist to clean that tree up.  Crossing branches need to be removed and the whole tree opened up for access to sunlight and breezes.  You can find the arborist you need by going to this link and clicking on Find An Arborist.  When prompted put in your zip code and a list of certified arborists in your area will appear.  They are all well qualified and participate in continuing education classes every year in order to maintain their certification.  

TreesAreGood.org