Code example of custom Magento 2 menu for adding thumnail images.
<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
<module name="Milandev_CustomMenu" setup_version="1.0.0">
<sequence>
<module name="Magento_Catalog"/>