gistfile1.txt

    |
[a] *
    |
[b] *
    |\
[c] * \
    |  \
[d] *   * [f]
    |   | 
[e] *   * [g]
    |   |
  [foo] * [h]
        |
      [bar]

Given I'm on bar/HEAD, is there a way for git-log or some other git command to know that "the start" 
of this branch is [b]? (without knowing that the branch stems from foo, so `git log foo..bar` 
doesn't work for me)