Multics had much more complex security, with access-control lists.
The authors of Unix have taken most of the concepts of an hierarchical file system from Multics, the main exception being the security features, which have been replaced with the simpler owner-group-all permission bits, together with features like setuid/setgid, which may be OK for simple use cases but which is inadequate for a system with many users, where not all of them can be trusted.
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Multics had much more complex security, with access-control lists.
The authors of Unix have taken most of the concepts of an hierarchical file system from Multics, the main exception being the security features, which have been replaced with the simpler owner-group-all permission bits, together with features like setuid/setgid, which may be OK for simple use cases but which is inadequate for a system with many users, where not all of them can be trusted.