$ git show --first-parent main
commit 59d314ad6f356dd08601a4cd5e530381da3e3c64
Merge: 9a6d494 c7a2ab9
Author: A U Thor <author@example.com>
Date:   Mon Jun 26 00:04:00 2006 +0000

    Merge branch 'side'

diff --git a/dir/sub b/dir/sub
index cead32e..992913c 100644
--- a/dir/sub
+++ b/dir/sub
@@ -4,3 +4,5 @@ C
 D
 E
 F
+1
+2
diff --git a/file0 b/file0
index b414108..10a8a9f 100644
--- a/file0
+++ b/file0
@@ -4,3 +4,6 @@
 4
 5
 6
+A
+B
+C
$