exchange/app/Http/Controllers/Api/DocumentCategoryController.php

<?php

namespace App\Http\Controllers\Api;

use App\Models\DocumentCategory;
use App\Transformers\CategoryTransformer;

class DocumentCategoryController extends ApiController
{
    public function index()
    {
        $categories = DocumentCategory::orderBy('lft', 'asc')->get();
        return $this->respondWithCollection($categories, new CategoryTransformer($this->locale, 'trading'));
    }
}