Answer: Unfortunately, this type of damage is very difficult, if not impossible, to repair because a "double trunk" is intrinsically weak. Also, at ground level, the split will get wet regularly, promoting rot, which you are already seeing. You basically have two choices. One would be to remove it and replace it, the other would be to cut it off at ground level below the split, at a 45 degree angle, within a 1/4" of a side shoot or bud, and see if it will resprout from the roots next year. I'm sorry I can't be more encouraging.
Q&A Library Searching Tips