git-merge-consecutive.sh

#!/bin/bash
trap "exit 1" ERR

isPush=false
if [[ "$1" == "--push" ]]
then
    isPush=true
    shift
else
    isPush=false
fi

while [ $# -gt 1 ]; do
    git checkout $2
    git merge $1

    [ "$isPush" = "true" ] && git push

    shift
done  

if you have already some PRs waiting for review and they build all on top of each other, this utility comes in handy.

git-merge-consecutive branch-a branch-b branch-c

this will do

$ git checkout branch-b
$ git merge branch-a
$ git checkout branch-c
$ git merge branch-b

Heads up: Usually it is not the best idea to make branches dependent on each other while they are in review. Why? It can happen that one PR gets rejected so badly, that you would need to rewrite it completely. So there is a risk, that all consecutive branches / pull requests depend on something this will go into trash. But I am not your mother, and because you know what you are doing, you know when you can use this utility