LinuxQuestions.org - a strange fork in RHEL as4u2

I found a loopback fork in an redhat enterprise linux:
It's difficult for me to understand these things,
is there anybody give me some directions on this kind of loopback forking?

Code:

root      1754    1  0 Jan09 ?        00:00:09 /usr/sbin/sshd

root    26769  1754  0 Jan31 ?        00:00:00 sshd: cmil [priv]

cmil    26771 26769  0 Jan31 ?        00:00:00 sshd: cmil@pts/0

cmil    26772 26771  0 Jan31 pts/0    00:00:00 -bash

root    26796 26772  0 Jan31 pts/0    00:00:00 su -

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ATTACHED: I'm sorry. It's my fault that take 26796 as 26769, very sorry!