Bunk = SPECIFICALLY for school/college classes...
Tulla however can be used for anything, school college Uni, aaaaand Office....
Also, howmany here can successfully plan and execute an 'intelligent tulla' in classes? its like couple of small washroom breaks, quick jogs to the caffetaria and some other, slipping out as soon as the attendence is done, 'Sir talent show ki rehersal' etc etc