How to make MenuWidget in yii2 framework work?

Question

Yii

There is MenuWidget code:

<?php

namespace app\components;
use yii\base\Widget;
use app\models\Category;

class MenuWidget extends Widget{

    public $tpl;
    public $data;
    public $tree;
    public $menuHtml;

    public function init()
    {
        parent::init();
        if ($this->tpl === null) {
            $this->tpl = 'menu';
        }
        $this->tpl .= '.php';
    }

    public function run()
    {
        $this->data = Category::find()->indexBy('id')->asArray()->all();
        $this->tree = $this->getTree();
        $this->menuHtml = $this->getMenuHtml($this->tree);
        return $this->menuHtml;
    }

    protected function getTree()
    {
        $tree = [];
        foreach ($this->data as $id => &$node) {
            if (!$node['parent_id'])
                $tree[$id] = &$node;
            else
                $this->data[$node['parent_id']]['children'][$node['id']] = &$node;
        }
        return $tree;

    }

    protected function getMenuHtml($tree)
    {
        $str = '';
        foreach ($tree as $category) {
            $str .= $this->catToTemplate($category);
        }
        return $str;
    }

    protected function catToTemplate($category)
    {
        ob_start();
        include __DIR__ . '/menu_tpl/' . $this->tpl;
        return ob_get_clean();
    }
}

And there is a broken line in index.php for MenuWidget:

• 
  <?= \app\components\MenuWidget::widget(['tpl' => 'menu'])?>
  

If you make a mistake in something in the code, the program will report this, but now, it would seem, there are no reasons for errors, but it’s as if I didn’t write anything for the widget