this is vastly overstated imo. on most issues the left is pretty unified.
orange man bad, clinton woman good, police bad, welfare state good, white people bad, brown people good, russia bad, muslims good, believe wahmen, diversity is great, etc.
the friction you see around figures like omar and cortez (and sanders to a certain degree) is just mild internal disagreement about PR issues and optics, not fundamental differences in values or policy. they're all aboard the same train, they only disagree about how fast they want to go there and how honest they want to be about it to the public at this point.