Today I just raised a Berserker to 20 and rolled his perks 4 times.
Now he have +15 VIT, +15 VIT, +10 STR.

Too bad he had sh*tty stat grow on his level-ups.
36 STR, 47 VIT, 20 GRT

So in 20 levels he gained 21 STR, 17 VIT and 20 GRT.