Yii2 Widgets - how to remove duplicate parent menu category?

Question

Yii

Hello!
I have a problem with Yii2. I learned how to work with the basic part, but it’s a real problem with widgets, I don’t understand them, help me out!
There is a widget:

Code (zhmyak)

class MenuWidget extends Widget{

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

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

    public function run(){
        // get cache
        if($this->tpl == 'menu.php'){
            $menu = Yii::$app->cache->get('menu');
            if($menu) return $menu;
        }

        $this->data = Category::find()->indexBy('id')->asArray()->all();
        $this->tree = $this->getTree();
        $this->menuHtml = $this->getMenuHtml($this->tree);
        // set cache
        if($this->tpl == 'menu.php'){
            Yii::$app->cache->set('menu', $this->menuHtml, 60);
        }
        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']]['childs'][$node['id']] = &$node;
        }
        return $tree;
    }

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

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

}

Widget (click)

<li class="group-item">
    <a href="<?= \yii\helpers\Url::to(['category/view', 'id' => $category['id'], 'slug' => $category['slug']]) ?>">
        <?= $category['name']?>
    </a>
    <?php if( isset($category['childs']) ): ?>
        <div class="group-tree-icon expand"></div>
        <ul class="sub-groups-list">
            <?= $this->getMenuHtml(($category['childs']))?>
        </ul>
    <?php endif;?>
</li>

The problem is <?= $this->getMenuHtml(($category['childs']))?>I don't know how to make another code for subcategories, everything is duplicated from the parent. Save
How should I write so that I can write another code for subcategories?