/usr/lib/ghc-doc/hoogle/libghc-tree-monad-doc.txt is in libghc-tree-monad-doc 0.3-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-tree-monad-doc/html/tree-monad.txt