Do not put anything too thick on the cut, as it can retard regrowth of the bark over the cut scar. We used to use clear laquer spray paint (when I was a landscaper) , as the wood can protect itself within a few weeks or months after the cut. Also, remember on some trees that rot easily, you may want to insure that the cut can drain well by cutting a vertical slot in the cut. When the middle of a cut branch begins to rot, water pools in it accelerating the rot, which can extend into the tree trunk. Note that this still can happen underneath a tar - covered cut scar.