The range started with PopStar, Easy, Lounge & Trekking. However, Easy was dropped. Presumably down to lower sales, though it also looked naff with steel wheels & wouldn't do overall resale value any favours when 3 year old ones start appearing with Halfords special wheel trims.
Fiat then added the entry level Pop and flagship Beats Edition. The Beats Edition being based on the Trekking but with extra kit and exclusive paint combinations. So the range is now:
Pop (wheel trims, no aircon, mostly a headline grabber to show off the price)
PopStar (alloys, aircon, chrome inserts on rubbing strips)
Lounge (as above plus climate control, panoramic roof, part suede interior)
Trekking (body cladding, bigger wheels, traction+, part leather interior)
Beats Edition (as above plus exclusive paint, black alloys, HiFi byBeats stereo)
The Easy had similar levels of kit to PopStar, but had wheel trims rather than alloys, plain black rubbing strips with no chrome, electric rear windows and upholstery with coloured squares on it, rather than the '500' badged cloth of Pop/PopStar, part suede of the Lounge or part leather of the Trekking/Beats.