How do I 'overwrite', rather than 'merge', a branch on another branch in Git?

Question

I have two branches, email and staging. staging is the latest one and I no longer need the old changes in email branch, y

Answer 1

I tried @knittl's write-tree/commit-tree approach.

branch-a: the kept branch

branch-b: the abandoned branch

// goto branch-a branch
$ git checkout branch-a

$ git write-tree
6fa6989240d2fc6490f8215682a20c63dac5560a // echo tree id? I guess

$ git commit-tree  -p branch-a -p branch-b 6fa6989240d2fc6490f8215682a20c63dac5560a

20bc36a2b0f2537ed11328d1aedd9c3cff2e87e9 // echo new commit id

$ git reset --hard 20bc36a2b0f2537ed11328d1aedd9c3cff2e87e9