docz: Duplicated menu when using hierarchy

Bug Report

When adding sub-menu items, I’m facing an item both inside it’s parent and in the root level:

Here is the document configuration:

---
name: Composition
route: /concepts/composition
menu: Concepts
---

And here is the menus config:

// doczrc.js
module.exports = {
  menu: [
    'Introduction',
    'Getting Started',
    { name: 'Development', menu: ['Structure', 'Environment & Commands'] },
    { name: 'Concepts', menu: ['Composition'] },
    { name: 'Reference', menu: ['Routing', 'Layouts & Blocks', 'Menus'] }
  ]
}

Expected behavior

Once I configure an item to be shown under a parent, it should not be shown in the root level.