[Android Central Question]

I can only select one song and transfer it using Bluetooth but not able to select more than one.

[Rukbat]

That depends on the way you're doing it. Some Bluetooth file transfer apps allow you to select more than one file at a time. (They still transfer one at a time, but it's easier to pick the few you want to transfer, then be able to ignore the app until it's done transferring all of them.)