Asking git to look for different key other than id_rsa

I not sure why but even though I mention properly in ssh config to look for identity file with name viren.pub for github

git still considering id_rsa as default and it does not seem to work unless an until i rename viren.pub and viren to id_rsa.pub and id_rsa

Here my ssh config look like

Host [Amazon server]
         Hostname github.com
         User git
         IdentityFile /root/.ssh/viren
 

Can anyone help

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