Click on the "envelope" in the far-left top of the ATP Home Page.
It will be red if you have any unread Tree-Mails.
Or, click on the Subject of the email (middle-left top).
If the envelope is not reddish-pink, and there is no row that says you have an updated personal Tree-Mail, either it never got TO your Inbox, or the system thinks you have already read it.
You can click on the envelope even if it is not red.
That will bring you here:
If there is still no updated personal Tree-mail, click "Access your full Tree-Mail Inbox.
(It isn't "full", it's your entire Inbox, read and un-read alike.)