Narrative analysis: The vision of the tree comes after Lehi's desire for the mercy of the Lord. While the object of Lehi's desire is not clear in the Book of Mormon text, it follows the pattern of the Narrative of Zosimus, where the vision is the result of the desires of a righteous man: "About that time there was in the desert a certain man named Zosimus, [who for forty years ate no bread, and drank no wine, and saw not the face of man.] This man was entreating God that he might see the way of life of the blessed..." (Narrative of Zosimus p. 315).
In this context, it is clear that when Lehi prays for "tender mercies" he is interested in things of the Spirit, not personal comforts. Thus the dream of the tree comes precisely in response to this desire.