public function validateTree()
    {
        if (!$this->showTree) {
            return;
        }

        $this->showSorting = $this->showPagination = false;

        if (!$this->model->methodExists('getChildren')) {
            throw new ApplicationException(
                'To display list as a tree, the specified model must have a method "getChildren"'
            );
        }

        if (!$this->model->methodExists('getChildCount')) {
            throw new ApplicationException(
                'To display list as a tree, the specified model must have a method "getChildCount"'
            );
        }
    }