Reading and searching the first (and only) block of the aux-aux index which is the root of the tree identifies the relevant block in aux-index in the level below. Reading and searching that aux-index block identifies the relevant block to read, until the final level, known as the leaf level, identifies a record in the main database.
This describes how records are located in a hierarchical database structure using an index. The process starts at the root of the tree (the main index) and moves down to the leaf level (the final record).