bills_tree_upload_views.xml

<?xml version="1.0" encoding="UTF-8"?>

<templates>
    <t t-name="account.BillsHiddenUploadForm">
        <div class="d-none o_vendor_bill_upload">
            <t t-call="HiddenInputFile">
                <t t-set="multi_upload" t-value="true"/>
                <t t-set="fileupload_id" t-value="widget.fileUploadID"/>
                <t t-set="fileupload_action" t-translation="off">/web/binary/upload_attachment</t>
                <input type="hidden" name="model" value=""/>
                <input type="hidden" name="id" value="0"/>
            </t>
        </div>
    </t>

    <t t-extend="ListView.buttons" t-name="BillsListView.buttons">
        <t t-jquery="button.o_list_button_add" t-operation="after">
            <button type="button" class="btn btn-secondary o_button_upload_bill">
                Upload
            </button>
        </t>
    </t>
</templates>