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

<?php

namespace App\Http\Controllers\Api;

use App\Http\Controllers\Api\ApiController;
use App\Models\Category;
use App\Transformers\CategoryTransformer;

class CategoryController extends ApiController
{
    public function index()
    {
        $categories = Category::orderBy('lft', 'asc')->limit(2)->get();
        return $this->respondWithCollection($categories, new CategoryTransformer($this->locale, 'trading'));
    }
}