In odoo12 enterprise edition, I created a module, its all submenus are added to the top menu but not their parent menu.

In my code, first, I added the outsourcing menu to the website.main_menu and some submenu to the outsourcing menu. The result is that all submenus are added to the website.main_menu.
Another problem is that after uninstalling the module, there are unremoved submenu items in the menu of the website's configuration.

The following is my code. what is the problem?

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
    <data noupdate="0">
        <record id="main_menu" model="website.menu">
            <field name="name">Outsourcing</field>
            <field name="url">/outsourcing</field>
            <field name="parent_id" ref="website.main_menu"/>
            <field name="sequence">11</field>
        </record>
        <record id="issue_requirement" model="website.menu">
            <field name="name">issue task</field>
            <field name="url">/outsourcing/issue_task</field>
            <field name="parent_id" ref="outsourcing.main_menu"/>
            <field name="sequence">12</field>
        </record>
    </data>
</odoo>