Here is mine understanding about both
B Tree index :- It is generally used database column. It keeps the column content as key and row_id as value . It keeps the key in sorted fashion to quickly find the key and row location
Inverted Index :- Generally used in full text search. Here also word in document works as key, stored in sorted fashion along with doucument location/id as value.
So what's the difference b/w B tree index and Inverted index . To me they looks same