Custom button ListView - Odoo 15

With t-name
<t t-extend="ListView.buttons" t-name="HrExportListView.buttons">
    <t t-jquery="button.o_list_export_xlsx" t-operation="after">
        <button type="button" class="oe_export_ins">INS</button>
    </t>
</t>

Without t-name
<t t-extend="ListView.buttons">
    <t t-jquery="button.o_list_export_xlsx" t-operation="after">
        <button type="button" class="oe_export_ins">INS</button>
    </t>
</t>