Pyramid scheme: “you recruit five people to give you a dollar and those five recruit five more people to give them a dollar and those five recruits....”
MLM: “You recruit five people to give you a dollar and you given them a pixie stick. Those five recruit five more people to give them dollars for a pixie stick and those five recruit...”
The difference is just a loophole where the pixie stick or whatever stupid product they have (usually useless and always overpriced) somehow makes it legal.
The product they use is often something with a dubious health claim which in some ways makes them even more evil than a simple pyramid scheme