Can we consider bigmac as a burger?

Yes: As we often say in medicine, if it looks like a burger, smells like a burger, and tastes like a burger, then it is indeed a burger. It can be made healthier if ordered with "little or no sauce". It can be made lower in fat if ordered without cheese, but one also loses some protein that way, since cheese is half protein / half fat. If ordering the combo, choose a drink that has little or no sugar.