Obito can probably win by either locking kuarma in the barrier while charging BD outside .once it ends ,he removes the barrier and fires the BD at kuarma or by locking himself and the tree in the barrier with kuarma outside .once the charging ends ,he removes the barrier and fires the BD at kuarma.
The tree realese is an option too.
If obito can summon jiubi then that will be another option too .