Here's a breakdown:
* POH: The "o" sound is like the "o" in "go" or "no".
* uh: This is a short, unstressed vowel sound, like the "u" in "but".
* tree: This is pronounced like the tree we climb on.
There is a less common pronunciation, POH-uh-try, where the "y" sound is more emphasized.
Ultimately, both pronunciations are acceptable, but the POH-uh-tree is the most common and widely recognized pronunciation.