Most modern indexing structures are in the succinct radix tree algorithm family. This is a diverse algorithm space with many design knobs that can be used to optimize properties and behavior in multiple dimensions, so any two algorithm implementations can look quite different. Most algorithms of this type you see in the wild don't have names, they were designed to fit requirements from first principles.

You can find simple, albeit limited and not too succinct, examples of these types of data structures online. More advanced capabilities crammed into ever more succinct representations can quickly become difficult to reason about -- the code looks much more abstractly information theoretic and less like a traditional index.