Save the citations from Isaiah, Nephi's text which begins with the Tree of Life and ends with the abbreviated account of his apocalyptic vision is the longest extended text in the Book of Mormon. Nevertheless he indicates that he has written "but a small part of the things which I saw." Much of the missing description is absent on command.
This is a text written long after the event, and inserted in the body of a more or less "historical" account of the families exodus from Jerusalem. What is most interesting is that the trigger for the apocalyptic vision is the Tree of Life dream, but Nephi's account of his vision leaves behind the explication of the particular symbols rather rapidly, and expands to the Johnanine apocalypse. What is most interesting is that in the chapter to come (chapter 15) when Nephi returns to speak with his brothers, the questions return to the interpretation of symbols. This great vision is not even mentioned. In the context of the actual events, we have a dream, Nephi seeking an interpretation, and then explaining it to his brothers.
What is missing from that context is the great messianic vision. Certainly Lehi saw it, and included some of it. Certainly Nephi saw it - but there is less evidence that he specifically related what he saw. Why include the vision in the small plates account? As indicated before, the particular restrictions on writing appear to mark this vision for the latter day. It would have been immeasurably important and uplifting to Nephi, but it appears that the details were, at least at the time, not for public knowledge.