With release 3.4.14 for Windows you could rename a repo under the Local Repositories to show the value in the tab name. Updating to 3.4.15 the tab always displays the folder name and not the bookmark name which you can rename.
Before rename

After rename:

After you rename prior to 3.4.15 it would rename the tab to show "SourceTree Tab Name Project" and not keep what the folder name was called.