/// <summary>
 /// Retrieve category node hierarchy from the database.
 /// </summary>
 /// <returns></returns>
 private IList <CategoryNode> GetTreeHierarchy()
 {
     using (ResourceDataAccess dataAccess = new ResourceDataAccess(this.CreateContext()))
     {
         return(dataAccess.GetRootCategoryNodesWithHierarchy().ToList());
     }
 }