Please find code here :-

for example:
<template id="template_header_default" inherit_id="website.template_header_default">
<xpath expr="//t[@t-foreach='website.menu_id.child_id']" position="before">
<t t-set="categories" t-value="request.env['product.public.category'].sudo().search([])"/>
<t t-foreach="categories" t-as="categ">
<li class="nav-item">
<a t-att-href="'/shop/category/%s' % categ.id" class="nav-link">
<span t-esc="categ.name"></span>
</a>
</li>
</t>
</xpath>
<template>