[Бармалей]

Документацию читать внимательно 2 раза!!! =)

expandItem () method

Opens or closes a branch item. When a branch item opens, it restores the open and closed states of its child branches if they were already opened. If you set dataProvider and then immediately call expandItem() you may not see the correct behavior. You should either wait for the component to validate or call validateNow() .