This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
桵 combines 木 (tree) with 妥, but the historical origin and meaning are uncertain. It may be a phono-semantic compound, but the exact development is unclear.
With no clear meaning, picture a tree 木 beside something peaceful 妥, perhaps a tree that brings calm, but its true meaning is unknown.
For ズイ, imagine a zany tree: zany -> ズイ, though the tree's purpose is a mystery.