git remove merge commit from history

My Git history looks like that :

I would like to squash the purple commits into a single one. I don't want to see them ever again in my commit log.

I've tried to do a git rebase -i 1, but even though 1 is on the blue branch (cf. picture), I still see every commit on my purple branch.

How can I completely remove the purple branch (from commit log) ?

Do git rebase -i <sha before the branches diverged> this will allow you to remove the merge commit and the log will be one single line as you wanted. You can also delete any commits that you do not want any more. The reason that your rebase wasn't working was that you weren't going back far enough.

WARNING: You are rewriting history doing this. Doing this with changes that have been pushed to a remote repo will cause issues. I recommend only doing this with commits that are local.