Superman and Batman enter the Cosmic Tree, but split up again in the penultimate chapter of this story, by Kraft, Colan and Mitchell, in World’s Finest 299 (Jan. 84).
Colan does an excellent job on this tale. Batman winds up at the “temple” at the top of the Tree, while Superman is down at the base. They each hear variations on the same tale, which basically comes down to: The Cosmic Tree brings life to different planets, but kills and replaces the pre-existing life. It provides sustenance for its people, but causes an endlessly expanding civilization, who have to take over new worlds simply to sustain themselves.
All this means that Earth is doomed, although to stop the Tree spells death for those it nurtures.
Superman climbs up the Tree as Batman climbs down. They meet and compare notes. They had passed Zeta on the way in, I ought to have mentioned that, but the creature is sitting in meditative contemplation.
Batman has pretended to be on the side of those in the Temple, to gain their trust, and information. The Temple become suspicious when they see him working with Superman, from the bottom of the Tree. Batman insists he was just about to execute him (as per the cover), but in reality gets Superman out of the Tree and back to Earth.
The story concludes in the giant sized anniversary issue the following month.