The top of your tree rose is the "bud union" and it must be protected from the cold of zone 6. Winter protect it in some way. There are different methods to do this, you may choose to bury the entire plant in a trench below ground and unearth it every spring, or you may want to bring it in to an unheated 3 season room/garage (this requires you to continue to moniter its water needs), or you could pack the "bud union" with a dry mulch and wrap with burlap. Good luck.