Not really. Best you can do is add Categories to spaces to group them.
Otherwise, you can link to pages in other spaces. In fact, you could use the Include Page macro to create a set of pages in a space that pull from different spaces to give the impression of a hierarchy.
I'd like to know which use cases you have in mind for creating a hierarchy of spaces?
If it's just to group them, categorizing - as mentioned by Milo and Rodney - is typically the solution.
The uses cases for page hierarchies are probably a handy method to move/delete a page tree or to limit searches within the child hierarchy.
The projectdoc Toolbox - which is our product - allows to define space hierarchies with delegate spaces to inherit space properties or to share document homepages (e.g. to have all glossary entries for a set of spaces at one location). You may also define search spaces to limit search results of macros. Space Hierarchies provides a short introduction in these concepts.
But these two features are not supported by Confluence, so this is probably not your use case ...?
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