ssh config not working. Permission denied (publickey)

I am having trouble with my ssh config. I had multiple key pairs and multiple host so I want to setup ssh config so that I can easily switch between them.

My ssh config looks like this:

Host blog
    User Myusername
    HostName github.com
    IdentityFile ~/.ssh/macbook_id_rsa

Host blog2
    User Myusername2
    HostName github.com
    IdentityFile ~/.ssh/macbook_2_id_rsa

now, if I just add my private key using ssh-add and enter passphrase, I am able to connect to github or other host. But When I try to switch different key pair like

ssh -vT blog

I got error message like this:

OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
debug1: Reading configuration data /Users/paul/.ssh/config
debug1: /Users/paul/.ssh/config line 1: Applying options for blog
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug1: Connecting to github.com [192.30.252.130] port 22.
debug1: Connection established.
debug1: identity file /Users/paul/.ssh/macbook_id_rsa type 1
debug1: identity file /Users/paul/.ssh/macbook_id_rsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
debug1: Remote protocol version 2.0, remote software version libssh-0.7.0
debug1: no match: libssh-0.7.0
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-sha1 none
debug1: kex: client->server aes128-ctr hmac-sha1 none
debug1: sending SSH2_MSG_KEXDH_INIT
debug1: expecting SSH2_MSG_KEXDH_REPLY
debug1: Server host key: RSA 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
debug1: Host 'github.com' is known and matches the RSA host key.
debug1: Found key in /Users/paul/.ssh/known_hosts:3
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/paul/.ssh/macbook_id_rsa
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

Can anyone point out if I did something wrong with my ssh config, or what am I missing here. Thank you

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