Here is the full list of all 12 Infestor achievements worth 1,000 gamerscore. It takes around 0.5-1 hour to unlock all of the achievements on Xbox One.
Complete level 50.
Complete level 40.
Take control of a Jet Scouts.
Complete level 30.
Take control of a Overseer.
Complete level 20.
Destroy a droid.
Destroy a Turret.
Take control of a Guard.
Complete level 10.
Take control of a Worker.
Take control of a Colonist.