A tab has two combo boxes. The first one is the parent of the second one. The second one is the sub of the first one. It displays values for each item in the first combo box. That means each item in the first combo box has sub values in the second combo box.

How do I prepare the coding or set anything else (in the properties) or sth so that for each item in the parent combo box, ONLY the sub values of that parent is displayed in the second combo box.

The reason for this question is because for a parent item, the sub values of other parent items also appear in the second combo box.