Jonas there are as far as I am concerned 3 main patterns, but there are examples of 'variations'. These variations do appear on period imagery and are often a repair or a modification of the 3 main types. Either way having a bipod, whatever type it was, in the middle or near middle did not make it a very stable firing platform, hence the inter-war modification.
I will post some images and mention the differences. If other members have some imagery of unusual bipods that would be very useful too.
Mark