This winter was very harsh with temperatures fluctuation between the teens and up to 40 degrees, then down to the teens again and up to the 50's and even 60 degrees, only to drop down to minus 6 degrees.  Every time the temperature warmed up past 40 degrees the tree thought it should start to come out of dormancy, and sap would start to flow up from the roots to the leaf buds.  When the temperatures dropped down after the sun set, the sap and water would be caught in the xylem and would freeze.  Water expands when it freezes so the tree would have to expand as well.  When that happened, small cracks would form and sometimes they would expand up and down the trunk of the tree.  This is called a frost crack.  The best thing that you can do for your tree is to water it with 2-4 gallons of water at least once a week to help keep it hydrated and healthy.  The foliage looks great and the shape of the tree also looks healthy.  Also, please remove any weeds in the mulched area so they don't compete with the tree for the moisture.