first-parent equivalent for show-branch

[Jeenu V <jeenuv@gmail.com>]

Hi,

I wanted to know if there's a --first-parent equivalent for git
show-branch, where in it shows only the first -parents in a vertical
column. I feel it'd make the display less cluttered.

As of now, I think, a column shows commits in a merged branch, and
even parents of that branch, which makes reading bit uneasy. What
would be preferable instead to show only the first parent in a column
- something like the output of

git log --graph --pretty=oneline --abbrev-commit --first-parent --all
| sed 's#|\|/##g'

along with the header and naming strings of show-branch.

Thanks
-- 
:J