Assuming that a context-free tree language (CFTL) is that which is generated by a context-free tree grammar (CFTG), I am looking for an example of CFTL which can not be generated by a monadic CFTG (MCFTG).
In other words, I am looking for such a non-monadic CFTG for which it is not possible to construct an equivalent (MCFTG).
The all examples of CFTG's which exist in papers are essentially monadic CFTG.
I am still trying to build such a grammar by myself. But may be somebody already knows such an example and could share it as an answer. I deeply appreciate any help.