What does a bar six chocolate look like?

A "bar six" chocolate bar does not exist, so does not have a specific appearance. There is a Cadbury "Six Pack Kit Kat 41.5g" bar as well as several other products featuring the number six (or the Roman numeral) in combination with the word bar, chocolate, etc. Without further context specifying exactly what kind of chocolate-like confection they are referring to, the appearance can not be determined specifically.