What exactly turned Saruman to evil?

[BalrogRingDestroyer]

Was it:

1.) Greed and envy
2.) Messing with that Palantir too much and going to deep into the arts of Sauron
3.) A desire for more wisdom so he could help Middle Earth, and he believed that the Ring was the best means to it (in this regard, Saruman wouldn't have been lying when he said to Gandalf that it would be best if the Ring were controlled by one of them so that the Wise could direct Middle Earth and bring it to be run better (the very folly that lured Sauron to the Dark Side in the First Age.)

 

[Rebecca Fike]

I totally agree with the above points you had mentioned, may be their other thing that make him to evil.

 

[Elaini]

There's one detail not mentioned yet. They have a history in common well before the Third Age because both used to be Maiar serving Aulë the Smith in Valinor, but then both turned to serve Melkor (Morgoth, the first Dark Lord), Sauron sooner and Saruman later.

Saruman: "What do you want now, Mairon?"
Sauron: "Curumo, don't tell me you don't remember. We used to be workmates. There is something important I must tell you..."