Long term schengen VISA with less than 90 days stay

[Jaymin M Dhimar]

As I like to travel around the world and I am living in London on Tire 2, I already got three time schengen visa, but I am looking to get longest term visa with multi pal entry, so I can travel in Schengen member country as bagpacker, without any planning.

Can you please inform me, how can I apply for long-term visa with multipal entry and less than 90days stay.