The Bunu (Punu) are the

Yao people The Yao people (its majority branch is also known as Mien; ; vi, người Dao) is a government classification for various minorities in China and Vietnam. They are one of the 55 officially recognised ethnic minorities in China and reside in ...

who speak Hmongic languages. That is, ''Bunu'' in the broad sense is a cultural rather than linguistic group. Strecker (1987) had classified Bunu proper (Bu-Nao) as a Western (Chuanqiandian) Hmongic language, and the other Bunu (or ''Punuic'') languages— Younuo, Wunai (Hm Nai), and Jiongnai (Kiong Nai)—as distinct branches of Hmongic.Strecker, David. 1987.
The Hmong-Mien Languages
" In ''Linguistics of the Tibeto-Burman Area'', 10 , no. 2: 1-11. Matisoff (2001) grouped all of these together in a ''Bunu'' branch of Hmongic (that is, outside Western Hmongic). Ratliff (2010) returned Bunu proper (Bu-Nao) to Western Hmongic, and moved Jiongnai to its own peripheral branch of Hmongic, but did not address Younuo or Wunai.Ratliff, Martha. 2010. ''Hmong–Mien language history''. Canberra, Australia: Pacific Linguistics. Mao Zongwu (1997) found that Younuo, Wunai, and Pa-Hng form a distinct branch of Hmongic. The Bunu languages form a group in Chinese classification, but that is because Chinese classifications are not purely linguistic, but take into account ethnic identity.Wang Fushi, cited in Strecker (1987b)
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References

Hmongic languages Languages of China {{HmongMien-lang-stub