Treeview menu render twice categories in Laravel

I have created nested treeview categories and subcategories but seems that it is rendering the categories twice.

This is what is happen and I see on page.

Main category 1
  - Sub -category 1.1
  - Sub -category 1.2
Main category 2
  - Sub -category 2.1
  - Sub -category 2.2
Sub -category 1.1
Sub -category 1.2
Sub -category 2.1
Sub -category 2.2

What is happening here is that first is render the correct treeview but then under is render sub-categories as main categories.

The categories and sub-categories are saved in one table where I have column parent_id 0 for main category and if is sub-category is the id of main-category instead. This is my model

public function parent()
{
    return $this->belongsTo('App\Category');
}

public function children()
{
    return $this->hasMany('App\Category', 'parent_id');
}

Controller

public function index()
{
    $allCategories = Category::with(['children'])->get();     
    return view('categories', compact('allCategories'));
}

and the blade

@foreach($allCategories as $category)
  <li class="treeview">
    <a href=""></a>
    <ul class="treeview-menu">
      @foreach($category->children as $subcategory)
        <li class=""><a href=""></a></li>
      @endforeach
    </ul>
  </li>
@endforeach

via Chebli Mohamed