R&D is right about not using pressure treated lumber indoors, especially when tile is being installed. PT is too wet, and yes it'll shrink and twist as it dries out. Use only kiln dried lumber.
Having said that, the entire method of sleepers over concrete is not an approved method to build up a floor for the purpose of installing tile. It may work most of the time if everything is done well, but it's a high failure installation. You are likely to develop some bounce and you will trap moisture.
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.
If the whole reason for raiseing the floor is the cold then save what you would spend on wood ,sealer and backer ,and just get a floor heating system and tile to the slab.Thats what I did and it worked great