如何在Laravel中获取父类别的所有子类别？

// 父类别模型 Category.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Category extends Model
{
    protected $table = 'categories';

    public function subcategories()
    {
        return $this->hasMany('App\Models\Subcategory', 'parent_id');
    }
}

// 子类别模型 Subcategory.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Subcategory extends Model
{
    protected $table = 'subcategories';

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

$categoryId = 1; // 父类别的 ID

$category = Category::find($categoryId);
$subcategories = $category->subcategories;

foreach ($subcategories as $subcategory) {
    echo $subcategory->name;
}