Gen 2–3 — two trees, two choices, the expulsion
Both trees stood in the midst of the garden (Gen 2:9). Free access to every tree including the tree of life; only the tree of knowledge was forbidden (Gen 2:16–17). After the choice, God's stated reason for expulsion is the tree of life: "lest he put forth his hand, and take also of the tree of life, and eat, and live for ever" (Gen 3:22–24). Cherubim and a flaming sword bar access from that moment. Whether Adam and Eve had eaten of the tree of life before the fall is genuinely uncertain from the Hebrew text — Gen 3:22's grammar reads most naturally as future-contingent; Jewish tradition (Rashi) at points reads differently.