"True odds" just means letting it ride on each additional bet. Imagine $100 bet on each game, so if you parlay two games at -200, it would be $100 to win $50, then $150 to win $75, so you end up with $225, or +125
If it was three teams each at -200, the next game would be for 112.50, making the odds +238. And so on. You can do that with any numbers, + or -