Not a git gui client but you can do this via the command line with: git merge-base <branch1> <branch2>. This will give you their common ancestor. You can also

Not a git gui client but you can do this via the command line with: git merge-base <branch1> <branch2>. This will give you their common ancestor. You can also get something similar to the tig output but for specific branches via the command line using a command like: git log --graph --oneline <branch1> <branch2>.