diff --git a/demos/gtk-demo/tree_store.c b/demos/gtk-demo/tree_store.c
index 67d81bf..875d488 100644
--- a/demos/gtk-demo/tree_store.c
+++ b/demos/gtk-demo/tree_store.c
@@ -74,9 +74,12 @@ iterate_node(GtkTreeStore *model,
              TreeItem    *item_parent,  TreeItem    *item_children,
              GtkTreeIter *iter_parent,  GtkTreeIter *iter_children)
 {
-  printf("parent, children : %s -> %s\n", item_parent->label, item_children->label);
-  /* gtk_tree_store_append (model, &child_child_iter, &child_iter); */
-  /* gtk_tree_store_set (model, &child_child_iter, COLUMN_0, item_2->label, -1); */
+  printf("parent, children : %s -> %s    %p -> %p    %p -> %p\n",\
+         item_parent->label, item_children->label,\
+         iter_parent, iter_children,
+         &iter_parent, &iter_children);
+  /* gtk_tree_store_append (model, &iter_children, &iter_parent); */
+  /* gtk_tree_store_set (model, &iter_children, COLUMN_0, item_children->label, -1); */
   return GTK_TREE_MODEL (model);
 }