Given the severe weather we experienced this year, it may take a little longer for trees to leaf out. However, it looks like 1) There is no green or buds at all on the rest of the main tree 2) The branches look dry and lifeless  3) This is quite a large tree.  

Given these conditions and the size of the tree, I fear that it is in decline and may eventually pose a safety hazard if it dies.  I suggest contacting a certified arborist who can make an onsite assessment and provide a treatment plan.   They can also assist with removal and replacement if necessary. Many arborists will provide an initial assessment/quote for free. You can search for an arborist in your area here: https://www.treesaregood.org/findanarborist/findanarborist