We rebuilt the bulkhead walls because they were caving in. I felt it was due to tree roots but someone else told me it was from winter cold and frost. We have a wooden door on the outside of the bulkhead and a wooden door at the basement entrance from the steps. I was told to leave the inside door open during the winter to prevent frost heave. This makes the basement too cold. Does anyone have an opinion on the cause of the cement bricks and granite caving in? Does anyone have any suggestions on how to prevent the damage from recurring without letting the cold air in and the warm air out? Thank you.