Found the answer to this problem...
Here's the easy fix that came with upgrading to Android 6.0 on Nexus 5. When you connect your phone to the laptop, there is a notification that shows on the phone (when you slide your finger from top-down) that reads 'USB for charging, Touch for more option". Now touch that notification and you will go to a pop up screen with several radio buttons " Use USB for - charging only, transfer file (MTP), transfer photo(PTP) and MIDI". now choose MTP and your problem solved.