Android Marshmallow got many new security features also in view to USB-connection to PC handling. So enabling MTP in Android version six has proven to be problematic. You have to allow MTP or PTP every time, you connect your marshmallow’ed device to PC via USB.
This app makes it as convenient as possible. MTP Enabler allows you to select your desired mode with just a few clicks.
MTP enabler PRO Marshmallow v3.4.20160722 Apk