Getting SSH Key for Gitlab & Source Tree

Step 1 : Generate id_rsa public key by typing  : ssh-keygen -t rsa -b 4096 -C "youremail@com" on your command prompt.

Step 2 : Now open public key file and copy paste to gitlab at the ssh key section.

Step 3 : After that go to source tree and navigate to Tools > Add SSH key

Step 4 : Then check the connections  via "ssh -v git@gitlab.com"

Step 5 : If success,  you can now clone , pull, push or check out within your branches.

Step 6 : Otherwise, try git CLI to get it done manually if (Source Tree) problem occurs.

Source Reference :

https://help.github.com/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/