While crossing branches are a common problem they can be prevented with a little pruning each year. This pruning should occur on most trees in the winter months when they are dormant and threats of disease or bug infection is at a minimum. Dormancy makes it easier to see the braches and determine the best ones to remove. Some trees naturally have more crossing branches; while it is nice to get all of them, there are certain trees where it is almost impossible to get them all. A rule of thumb is to never remove more than a quarter of the trees crown in one season giving it time to grow and recover before more pruning is done. When you are finished making the pruning cuts, there is no need to put anything on the fresh wounds. In fact if a wound is sealed it is more likely that something can be sealed inside and cause a wound to fester rather than heal. Let the tree seal its wound naturally! Below is a diagram of how to properly make a large cut so the tree will seal the wound and recover correctly.
