app-odoo/app_hr_ztree/views/hr_views.xml

<odoo>
  <data>
    <!-- hr -->
    <record id="app_view_department_form" model="ir.ui.view">
        <field name="name">app.hr.department.form</field>
        <field name="model">hr.department</field>
        <field name="inherit_id" ref="hr.view_department_form"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='parent_id']" position="attributes">
                <!-- Add your fields or attributes here -->
                <attribute name="widget">ztree_select</attribute>
                <attribute name="options">{'ztree_parent_key': 'parent_id','ztree_expend_level': '1', 'ztree_name_field': 'name'}</attribute>
            </xpath>
        </field>
    </record>
    <record id="app_view_employee_form" model="ir.ui.view">
        <field name="name">app.hr.employee.form</field>
        <field name="model">hr.employee</field>
        <field name="inherit_id" ref="hr.view_employee_form"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='department_id']" position="attributes">
                <!-- Add your fields or attributes here -->
                <attribute name="widget">ztree_select</attribute>
                <attribute name="options">{'ztree_parent_key': 'parent_id','ztree_expend_level': '1', 'ztree_name_field': 'name'}</attribute>
            </xpath>
        </field>
    </record>
  </data>
</odoo>