protected function renderToolbar()
    {
        $lines = [];

        $lines[] = Html::beginTag('div', ['class' => 'btn-group']);

        $title = Module::t('message', 'Create a root node');
        $lines[] = Html::button(Module::t('message', 'Create'), [
            'title' => $title,
            'aria-label' => $title,
            'data-action-name' => 'create',
            'class' => 'btn btn-success',
            'onclick' => '{location.href="' . $this->createUrl('create') . '"}',
        ]);
        $lines[] = Html::button(Module::t('message', 'Collapse all'), [
            'id' => 'collapse-all',
            'class' => 'btn btn-default',
            'style' => $this->clientOptions['startCollapsed'] ? 'display: none' : 'display: block',
        ]);
        $lines[] = Html::button(Module::t('message', 'Expand all'), [
            'id' => 'expand-all',
            'class' => 'btn btn-default',
            'style' => $this->clientOptions['startCollapsed'] ? 'display: block' : 'display: none',
        ]);

        $lines[] = Html::endTag('div');

        return implode("\n", $lines);
    }