Doesn’t seem much of an improvement over what you have to do in a relational database
 or document database
You can do that exact thing the “hash” way, or the “set + hash” way, both of which are very easy. These aren’t the only ways to do it, just the couple ways that made the most sense to me without thinking too hard about them (and having an idea about what Redis offers).
As a side note, I think the proposed solutions are missing to consider an important aspect: update operations. If these trees are (almost) read-only then a simple JSON-encoded string can be enough. For (large) trees requiring frequent updates, Redis might not be the right tool at all — in this case I’m pretty sure graph databases would excel.