small bug fix

bintree.c

@@ -89,7 +89,7 @@ void *nextTreeData(TreeNode *root)
 // Releases all memory resources (including data copies).
 void clearTree(TreeNode *root)
 {
-    if (root == NULL) {
+    if (root != NULL) {
         clearTree(root->left);
         clearTree(root->right);
         free(root->data);