Answer:
Its title means book.
What has roots as nobody sees, is taller than trees. Up, up it goes, and yet never grows?
The more of it there is, the less you see.
An open ended barrel, it is shaped like a hive. It is filled with the flesh, and the flesh is alive.
What flies forever, Rests never?
I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?