本

Don't confuse with

All four are built on 木 (mù, tree). 木 alone is the plain tree — trunk, branches, roots, nothing added. 本 (běn, root/origin) adds a short stroke low on the trunk, marking the roots. 未 (wèi, not yet) and 末 (mò, end/tip) both add a stroke near the top, among the branches — the difference is which of the two top strokes is longer: in 末 the topmost stroke is longer (a tree's very tip, wide and open); in 未 it's shorter (branches that haven't fully grown out yet).