Scipio, I think you are correct that no Australian has ever been tried for treason. While Arbib may have been assisting a foreign power I think it very unlikely he would be tried for treason.
Other Australians who have served foreign powers include David Hicks and Dragan (Serbia) recently. During WW2 Barker, Chipchase and Stokes served with the SS.
During the cold war a few CPA members were exposed as Soviet agents ( eg Clayton).
I think Arbib is unique in being the only minister exposed.
Arbib joins an exclusive group but is unlikely to be to be tried for treason.
