Initial state:
==============

A - B - C - D - E - F - G - H  master
             \
              \
               I - J - K - L  feature


MERGE 1 : After git checkout master; git merge feature:
=======================================================

A - B - C - D - E - F - G - H - M  master
             \                /
              \              /
               I - J - K - L  feature


MERGE 2 : After git checkout feature; git merge master:
=======================================================

A - B - C - D - E - F - G - H  master
             \               \
              \               \
               I - J - K - L - M  feature