The Genesis Quest

The Genesis Quest is a science fiction novel written by Donald Moffitt first published in 1986, part of a two part series, the conclusion of the story being offered in Second Genesis.

Warning: Wikipedia contains spoilers

The Genesis Quest gets round the problems involved with intergalactic travel, namely the distance, by avoiding the traditional staple of science fiction, the warp drive. Instead Moffitt opts for a different tactic, that of having an alien race (The Nar) assemble humans from a stream of information beamed out from earth. The resulting colony of humans spend some time integrated into the Nar society before growing restless, and embark on the seemly impossible mission of a physical journey back to earth. This epic journey is made in a gigantic, space-grown semi-sentient tree, known as Yggdrasil.