Sourcetree will order it's graph by the date of commit/author only. It will ignore the parent/child context.

In my example

• 1.1 is the root of the branch
• 1.1.1.1 is child of 1.1
• 1.1.1.2 is child of 1.1.1.1
• ...
• 1.1 and 1.1.1.1 do have the same commit timestamp

GitExtensions order is correct
SourceTree order is wrong