For liars:
If that person happens to have a treasure in the box, he should say "the treasure is in my box" when he lies, then he tells the truth and becomes a liar; If he says "the treasure is not in my box", then he will speak according to your meaning and won't lie to you, so he will be in a dilemma and you can judge that the treasure is in his hand.
If there is no treasure in that person's box and the liar can only say "the treasure is in my box" to your question, then the rest of the people will never answer yes again and become forced to lie. From this we can determine who is lying, and the problem will be solved.