SUPPORT-8728: fix case parent id = self id;

+ add sort order

frontend/src/ts/component/field/DropdownTreeViewComponent.ts

@@ -57,7 +57,7 @@ export class DropdownTreeViewComponent extends InputControl {
           this.items = res.map(value => new TreeviewItem(this.createTreeItem(value)));
           const rootItem = this.items[0];
           this.i18n.selectedItem = rootItem;
-          this.value = rootItem.value;
+          this.value = rootItem ? rootItem.value : rootItem;
           this.doCollapseLevel();
           this.cd.markForCheck();
         });