Issue

I copy the SSH URL for cloning it in my sourcetree, and paste the URL like this.

and as you can see, Repository Type give me "This is not a valid source path / URL"

The Content of Detail was like this

git -c diff.mnemonicprefix=false -c core.quotepath=false --no-optional-locks push
-v --tags --set-upstream origin renewal:renewal Pushing to github.com:user name/
Git-practice.git 
The host key is not cached for this server: github.com (port 22) You have no guarantee 
that the server is the computer you think it is. The server's ssh-ed25519 key fingerprint
is: ssh-ed25658 256　SHA256:+HiY3wvvV7TuJJhbpZisF/zLDA0zPMSvHdkr7UvCOqU If you trust 
this host, enter "y" to add the key to

Solution

Open command prompt
Execute the following command

 > "C:\Users\username\AppData\Local\SourceTree\app-3.4.12（change the last part to yours）
\tools\putty\plink.exe" -ssh -C -i "C:\Users\nyun\sourcetree\private.ppk" 
git@github.com:～～（paste the SSH URL here）

Then, it ask like "If you trust this host, enter “y”...", so enter "y".

Yay! did it!