Merge commit without squash vs with squash option

merge commits are just commit but the difference is they have more than one parents. as you know commits may or may not have parent commit, in fact the merge commit is the commit that have more than one parent commit.

The difference between the two kinds of merge are only different in the commit history (as you showed the logs in graph).

Let's illustrate by graphs. Assume the commit history as below before merging:

A---B---C---D  master
     \
      E---F---G  develop

Merge commit (multiple parents):

The command used is git merge branchname. It's the default way to merge two branches.

When you merge develop branch into master branch by Merge commit in SmartGit (git merge develop), the commit history will be:

A---B---C---D---M  master
     \         /
      E---F---G    develop

Simple commit (one parent, "squash"):

It merges two branches with --squash option, the command used is git merge branchname --squash.

--squash

Produce the working tree and index state as if a real merge happened (except for the merge information), but do not actually make a commit, move the HEAD, or record $GIT_DIR/MERGE_HEAD (to cause the next git commit command to create a merge commit). This allows you to create a single commit on top of the current branch whose effect is the same as merging another branch (or more in case of an octopus).

When you merge develop branch into master branch by simple commit in SmartGit (git merge develop --squash), it get the changes from develop branch into master branch as a new ordinary commit (as if a real merge happened), and the commit history will be:

A---B---C---D---M  master
     \                 
      E---F---G    develop