Getting a unique list

I'd like to know how to print a unique list of states from the data set 
below.  Thanks in advance.
A newbie.

<data>
 <level name = "starter">
    <process name = "TR">
       <state name = "NY">143</state>
       <state name = "CA">19</state>
       <state name = "FL">215</state>
    </process>
    <process name = "PD">
       <state name = "NY">61</state>
       <state name = "CA">721</state>
       <state name = "FL">518</state>
    </process>
 </level>
 <level name = "mediumr">
    <process name = "TR">
       <state name = "NY">709</state>
       <state name = "CA"1285</state>
       <state name = "FL">52</state>
    </process>
    <process name = "YF">
       <state name = "NY">8</state>
       <state name = "CA">0</state>
       <state name = "FL">9</state>
    </process>
 </level>
</data>

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