Do you mean this?I think the fruit is the very third eye. Remember Obito or Madara (I can't recall exactly) said when the flower fruit blooms, it reflects on the moon. Well we saw that Madara got the third eye by absorbing the tree and reflected the third eye on the moon. So I think Kaguya and Madara's third eyes are the very fruit of the tree. Therefore,he doesn't need to eat another fruit.
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He never said it was the fruit. He said the fruit only occurs once every millennium.
Also Hagoromo shown Naruto what the fruit looked like.
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