This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 桺 is uncertain. It visually contains 木 (tree) and 丣, but the component relationship is unclear.
The left side is a tree 木, and the right side 丣 looks like a sealed container. Without a clear meaning, picture a mysterious tree with a sealed jar hanging from it—its purpose unknown.
For リュウ, imagine a willow tree (柳, やなぎ) that shares the reading リュウ. The willow's long branches sway like the unknown tree 桺: リュウ -> リュウ.