Depends on what you want to call that which Unix did.  We stuck the
proc file system there before there was a plan 9.  Also, Unix had
devices as files, though a hierarchy of 1 is not that general.

There were various file systems on Unix, like the semantic file
system, that represented more than just files.  I remember similar
things also presented in Usenix over the years.

Then there was the Mumps computer system at the Mas General Hosp
built in 1969.  It was a system that presented an integrated
language and database where everything available to the language
was a persistent object.  Not hierarchical though.