I've had the treble twice.

Once at level 2, the other around level 5 or 6.

Had a couple of double's where I have lost in a final a few times too. I think level 2 is probably the easiest level to get the treble on really as you have quite a few inactive teams around you. As you go up the levels I think it gets harder and harder to do, as the more you go into the game the more likely you are to come across fellow players who have put time and effort in, instead of those that tried the game and left.

Over the past 6 months or so I've kind of not bothered with the main cup though and often was out after the first round. I'd play the game light until the league was sorted and focus on it then as I find a few days away from the game often increases my appetite to play it a little.