It's 3-3-1-3.
3 centre backs, a defensive mid and 2 wing backs at the back and the "un enganche y tres punta" up front.
As to why noone tried to emulate it I guess it's because it virtually impossible to make the wingbacks move inside and attack the channels with wingers staying wide as opposed to the more standard wingers moving inside and wing backs attacking the byline. I might be wrong though
Correct, there's been loads of threads of people trying to emulate Bielsa's famous 3-3-1-3 but it's virtually impossible because in Bielsa's tactics the WB's don't provide width...instead they cut inside to become playmakers of sorts in the middle and control possession there. Hence why Bielsa has always used very versatile players in these 2 positions because they need to be able to play as WB and DM/CM, someone like David Alaba or Asamoah or Vidal for example, an all rounder.
But... What about using the "WB's" in MC positions ? Bielsa likes to mix the roles, usually he used one direct runner (Isla) and an all-rounder(Vidal) so one of the MCs would be "central midfielder-attack" and the other Box to box. In defence they would man mark the opposition wide mids/wingers. Of course if we want to be Bielsa, we should only use 3 man defence against 2 strikers.