The first time that Macbeth commits a treacherous act is when he commits regicide by killing King Duncan in act 2, scene 2. The actual murder happens off-stage, but we see Macbeth enter with two bloody daggers and declare to his wife, "I have done the deed." This is treachery on the grandest scale, because he has killed and betrayed his king and has done so while he was supposed to be keeping him safe, as his host. This is an especially treacherous act because King Duncan was a good king.
