ensure that a grandparent exists when it is involved in the ballance

@@ -263,14 +263,16 @@ typedef enum {rbBlack=1, rbRed=2} TR_rbColor;
 			TR_TREE_ROTATE(left, (root), (node)->parent->parent);  \
 		}
 
-#define TR_TREE_BALANCE_INSERT(root, node)            \
-	while (1) {                                       \
-		TR_TREE_BALANCE_INSERT_CASE1((node))          \
-		TR_TREE_BALANCE_INSERT_CASE2((node))          \
-		TR_TREE_BALANCE_INSERT_CASE3((node))          \
-		TR_TREE_BALANCE_INSERT_CASE4((root), (node))  \
-		TR_TREE_BALANCE_INSERT_CASE5((root), (node))  \
-		break;                                        \
+#define TR_TREE_BALANCE_INSERT(root, node)               \
+	while (1) {                                          \
+		TR_TREE_BALANCE_INSERT_CASE1((node))             \
+		TR_TREE_BALANCE_INSERT_CASE2((node))             \
+		if (NULL != (node)->parent->parent) {            \
+			TR_TREE_BALANCE_INSERT_CASE3((node))         \
+			TR_TREE_BALANCE_INSERT_CASE4((root), (node)) \
+			TR_TREE_BALANCE_INSERT_CASE5((root), (node)) \
+		}                                                \
+		break;                                           \
 	}
 
 #endif // __TR_TREE_MACROS_H__