* "Tree of Unhappiness" is not a known literary work or concept. It's possible this is a misremembered title or a personal interpretation of a different poem.
* "Pau Low Nia" is not a Korean tree. This phrase is likely a misspelling or a misunderstanding of a term related to another culture.
To help me understand your question better, please provide:
* The full title of the poem you're referencing.
* The original source of the poem (author, publication, etc.).
* The context of the line "Pau Low Nia" within the poem.
Once I have this information, I can help you understand the belief mentioned in the poem.