Idle git question: how come so many "objects"?

So I just made a commit that touched four files in all six active
branches, and I see:

$ git push
Counting objects: 172, done.
Compressing objects: 100% (89/89), done.
Writing objects: 100% (89/89), 17.07 KiB, done.
Total 89 (delta 80), reused 0 (delta 0)
To ssh://git(at)gitmaster(dot)postgresql(dot)org/postgresql.git
35a3def..8a6eb2e REL8_1_STABLE -> REL8_1_STABLE
cfb6ac6..b0e2092 REL8_2_STABLE -> REL8_2_STABLE
301a822..0d45e8c REL8_3_STABLE -> REL8_3_STABLE
61f8618..6bd3753 REL8_4_STABLE -> REL8_4_STABLE
09425f8..0a85bb2 REL9_0_STABLE -> REL9_0_STABLE
c0b5fac..225f0aa master -> master

Now I realize that in addition to the four files there's a "tree" object
and a "commit" object, but that still only adds up to 36 objects that
should be created in this transaction. How does it get to 172? And
then where do the 89 and 80 numbers come from?

regards, tom lane