EMPLOYEE WAS PUSHING TREES OVER WITH A DOZER WHEN HE RAN UP ON A TREE TOO CLOSE TO EDGE OF SLOPE AND DOZER TIPPED OVER DOWN THE SLOPE AND ROLLED ALL THE WAY OVER. EMPLOYEE WAS WEARING SEATBELT AT TIME. EMPLOYEE WAS NOT SUPPOSED T0 BE PERFORMING THIS TYPE OF WORK AS HE WAS NOT TRAINED TO PUSH TREES.