Board Thread:Theories and Speculation/@comment-36006024-20180712180727/@comment-31099706-20180712181823

Well, from what is shown, the Shinju is made of chakra too, or made out of chakra, as Momoshinki explained. So I guess absorbing the tree will lead Madara to gain more chakra and power, and evolve the Rinnesharingan and gain complete immortalitu.

The tree also seemed to be the part Kaguya was inside, since she talked to Madara in it or something.