Comma concatenation for all unique node value based on

Hi
<LINE_ITEMS>
<LINE_ITEM>
<PRODUCT_NUMBER>1</PRODUCT_NUMBER>
<CUST_MSG>Y</CUST_MSG>
</LINE_ITEM>
<LINE_ITEM>
<PRODUCT_NUMBER>1</PRODUCT_NUMBER>
<CUST_MSG>Y</CUST_MSG>
</LINE_ITEM>
<LINE_ITEM>
<PRODUCT_NUMBER>1</PRODUCT_NUMBER>
<CUST_MSG>Y</CUST_MSG>
</LINE_ITEM>
<LINE_ITEM>
<PRODUCT_NUMBER>2</PRODUCT_NUMBER>
<CUST_MSG>N</CUST_MSG>
</LINE_ITEM>
</LINE_ITEMS>

My expected out is
<products>1 and 2.
depends on the CUST_MSG value I need to concatenate "," and respectively.

Thanks,
Senthil