After successfully cloning my repo from heroku and added another remote
1/ git clone git@heroku.com:[APP].git
2/ git remote add bitbucket ssh://git@bitbucket
First choose or create the key you want to use for pushing to Bitbucket. Let's say its public key is at ~/.ssh/bitbucket.pub
~/.ssh/config
: Host bitbucket.org
IdentityFile ~/.ssh/bitbucket