This. Just because the party is evil doesn't mean there should be party infighting and betrayal. That tends to ruin the game.
Evil people can be loyal and cooperate.
Yes, even Chaotic Evil people.
Of course, that's the real "secret" to successfully incorporating evil characters into a campaign; actually
incorporating them, make them "fit" by making the party and the campaign actually accommodate each other so that there is a unified party of the player characters with enough shared goals to explain long-term cooperation for at least as long as needed to achieve those goals.
If you get the process down, you can actually start including evil characters in parties primarily good-aligned, and vice versa, without so much friction as to destroy the party cohesion or derail the campaign.
One of my current campaigns actually happens to include a Neutral Evil character, while the rest of the party are either Lawful Good or Neutral Good. They have friction, yes, but the players realize that their characters don't actually know each others alignment so they have to view each other as if they weren't sure about what alignment represents.
For example, at the end of a recent encounter one of their enemies feigned surrender to try and create an opportunity to escape with what information and items he had, unknown to any of the party, stolen. The NE character didn't believe the surrender was genuine, while the LG character (and all the others) did. The NE character struck down the foe without hesitation, and the rest of the party, shocked by this because it's not how they expect people to behave, demand explanation why she did that horrible, cruel (evil) thing. She offered "He was lying, trying to steal from us." as her explanation. The LG character pushed further, though the rest of the party accepted that as a good enough explanation, saying "You couldn't have known that was true!" (because she, like everyone else before searching the dead would-be thief, didn't have any evidence of theft or lie)
But, rather than doing what seems typical (from other groups I've had in the past, and what stories I've heard of campaigns involving evil characters) and having the LG character refuse to associate with the NE character any further, or jumping straight to "kill the evil!" over-reaction, the LG player said "If I ever see you murder a man again, whether you have some hunch there's reason or not, I'll be forced to turn you over to the authorities." Which completely resolves the situation because the NE character, being NE, will only do what she thinks she can get away with, and she knows now that she can't get away with killing someone without justification
prior to the act. And the characters stick together still, many sessions since that incident, because their goals are aligned and they are more likely to succeed together than apart.