Large unique index size on text field

I have 25M documents where each one has a unique identifier. This identifier is a random 90 character text.

My data sources might generate the same message multiple times, so I have to create e unique index on this field to make sure I do not insert the same document twice. However, my index size is getting very large and it’s around 3.5 GBs!

I’m just wondering if there’s any other way to store this index more efficiently?

I believe storing this index as a Trie would reduce the size significantly, but I’m not sure if Mongo supports it.