I got the key. Here are the logs
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /root/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 279
debug1: Authentication succeeded (publickey).
Authenticated to bitbucket.org ([104.XXX.XXX.1]:22).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: pledge: network
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
PTY allocation request failed on channel 0
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
authenticated via a deploy key.
You can use git or hg to connect to Bitbucket. Shell access is disabled.