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//IncidentCategoryList is the list control
//In this example we are only showing child items of the datasourced item which are using a specific Sitecore template named 'IncidentCategory'

foreach (
    var categoryDropDownItem in
        DataSourceItem(IncidentCategoryItemId).Children.Where(z => z.TemplateName == "IncidentCategory"))
{
    IncidentCategoryList.Add(categoryDropDownItem.DisplayName);
}