[IMP] hr: add tree view in Departments action window (#13418)

Tree view was removed to hide the different view types display in enterprise as it was "cleaner" for a dashboard. Re-adding for import button.

Future versions will not display departments as dashboard but employees anyway.

addons/hr/hr_view.xml

@@ -465,7 +465,7 @@
             <field name="name">Departments</field>
             <field name="res_model">hr.department</field>
             <field name="view_type">form</field>
-            <field name="view_mode">kanban,form</field>
+            <field name="view_mode">kanban,tree,form</field>
             <field name="search_view_id" ref="view_department_filter"/>
             <field name="help" type="html">
               <p class="oe_view_nocontent_create">