navbar.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!-- Copyright 2017-2018 Tecnativa - Jairo Llopis
     License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl). -->
<templates>
    <t t-extend="Menu">
        <t t-jquery=".o_menu_apps" t-operation="after">
            <!-- Hamburger button to show submenus in sm screens -->
            <button
                class="o-menu-toggle d-md-none"
                data-toggle="collapse"
                data-target=".o_main_navbar .o_menu_sections"
            >
                <i class="fa fa-bars" />
            </button>
        </t>
    </t>
</templates>