I had to reinstall SourceTree. Google is normally faster for finding downloads than crawling through excessive cutesy marketing pages. I clicked the first link https://www.sourcetreeapp.com/ which appeared to be official. After downloading and running the app in MacOS X Catalina, I received the message:
“Sourcetree” can’t be opened because Apple cannot check it for malicious software.
I wondered why it wasn't verified, so I feared it could be a hijacked link. I deleted the download and went straight to atlassian.com and navigated to the product link https://www.atlassian.com/software/sourcetree. The page looked the same as sourcetreeapp.com, but downloaded version was 3.1.2 instead of 4.0 that I downloaded from sourcetreeapp.com. I was able to run the application without making a security exception.
You guys should do a better job of making sure your downloads and the pages they are loaded from, are consistent.