ITunes For Mac :: Tries To Add Entire Folder To Library

I'm having a problem with adding files to iTunes. When I try to add a file to my iTunes library, it will not let me go into the folder to select individual files. It tries to add the enter folder. For example, I have all my music on an external drive. When I click "Add to Library" it brings up the hard dive. When I try to click the hard drive, it does not show me any other folders. It just tries to add the entire drive. I've moved a folder of one musical artist to my desktop, but it does the same thing. Tries to add the entire folder. It won't let me delve deeper and select albums or individual songs.