You could add a "Once While True". But designing any even system like that wher eyou need to duplicate the same event for increment is not a good idea. Instead re-think how your going about it.
Think about how your end condition occurs. At your end condition call a Function called say "wave.start" with param a param equal to wave_current + 1
so
global or sheet group variable called
wave_current = 1
End Wave condition met(what ever that is)
Function.call("wave.start", wave_current + 1)
On Function wave.start
set Enemies to X
set wave_current = Function.Param(0) //<- notice how your updating wave_current
enemies health = current_wave * 50
following this line of design. then there is not check for your wave. Instead the health of the enemies are effected naturally as your waves increase rather than make wave exception codes. Which could cause design problems