m1
$ echo m1 >> test.txt
$ git add test.txt
$ git commit -m "first commit"
m2
$ echo m2 >> test.txt
$ git add test.txt
$ git commit -m "second commit"
checkout feature branch
$ git checkout -b feature
f1
$ echo f1 >> feature.txt
$ git add feature.txt
$ git commit -m "third commit"
f2
$ echo f2 >> feature.text
$ git add feature.txt
$ git commit -m "fourth commit"
checkout main branch
$ git checkout main
squash merge
$ git merge --squash feature
view
$ git log --graph --oneline