Board Thread:Naruto Discussions/@comment-1926479-20140528055515/@comment-17623-20140528145905

According to Madara's story, which was conveniently missing Kaguya being a pyscho-crazy, the Ten-Tails appeared after Kaguya ate the fruit and went on a rampage to get it's chakra back. But what if eating the tree linked Kaguya to the giant tree, and it was her ego that made the tree sentient? Again all theory, but that would explain why either Kaguya gained the Ten-Tails' third eye or rather how the Ten-Tails obtained Kaguya's third eye.

For added theorist fun, the as the Rinnegan/Sharingan got passed down the Sage's line, the Byakugan could have been passed down his brother's.