Open rebellion against the state is an act of treason. Simple.
Ok fine, that seems like a charge to me, but sadly and me, or anyone else aren't the ones who get to decide who is carrying out an open rebellion, its the country's judicial system.
It was wrong to just kill Bugti like that. He should have had a fair trial. I am sure if he really was a traitor, the court would have had no problems in proving he was one. This was another mistake Musharraf made.