Tree radical on the left — also 柏's indexing radical. Anchors the meaning directly: 柏 is the cypress tree, a hardy evergreen planted at temples and graves. Same radical family as 松 (pine), 柳 (willow), 桃 (peach) — every species name lives here.
Right side 白 supplies the sound: bái → bǎi with only a tone shift. Same phonetic appears in 拍 (pāi), 怕 (pà), 帕 (pà), 迫 (pò). A faint semantic hint may also be present — the cypress's pale, silvery wood — but the primary role is sound.
