I nwant to merge lower release branch to latest release branch to bring differences with sourcetree

[Pranali Ubale]

Hi everyone, I am new to sourcetree and looking for using it for upgrading say A branch to latest D branch and A branch does have few commits which are not part of D and need to retain it. So I am using merge branch option by keeping commit history, however I do not see changes are taking place. Also, with Diff between branch A and D I am not seeing all commits differences to check upon. I have changed diff tool option to see more commits, however it's not effective to locate massive commits in bucket to compare for. Can someone suggest how to get this one?

Branch difference we are looking at is huge could be more than 200+ commits involving massive file changes. Also, Merge option may result in conflict however that's not showing anything on sourcetree GUI.

Repo I am using is Git