Similar to what's described in SERVER-45570, the CollectionBulkLoader uses two MultiIndexBlock objects, to build the _id index and other indexes, and MultiIndexBlock::insert() to build the indexes document by document. Only MultiIndexBlock::insertAllDocumentsInCollection has a ProgressMeter, which is not the code path used.

This use case is rather different than usual since the CollectionBulkLoader is using two MultiIndexBlocks at once.