var newXml =@"
<reestr>
	<paymentTransaction xmlns='http://privilege.sbibank.ru/'>
		<tranId>ABCDEF</tranId>
		<tranSum>262</tranSum>
		<tranDate>2016-12-03T11:43:40.907+03:00</tranDate>
	</paymentTransaction>
	<paymentTransaction xmlns='http://privilege.sbibank.ru/'>
		<tranId>ZXCV</tranId>
		<tranSum>234.1</tranSum>
		<tranDate>2016-12-13T11:43:40.907+03:00</tranDate>
	</paymentTransaction>
	<paymentTransaction xmlns='http://privilege.sbibank.ru/'>
		<tranId>BNMF</tranId>
		<tranSum>7262</tranSum>
		<tranDate>2016-12-23T11:43:40.907+03:00</tranDate>
	</paymentTransaction>
</reestr>
";

        [XmlType("paymentTransaction")]
        public class PmtTransaction {
            [XmlElement("tranId")]
            public long TranId { get; set; }
        }

            XmlSerializer ser2 = new XmlSerializer(typeof(List<PmtTransaction>)
               , new XmlRootAttribute("reestr")
                );

            List<PmtTransaction> envelope;
            using (StringReader reader = new StringReader(newXml))
            {
                envelope = (List<PmtTransaction>)ser2.Deserialize(reader);

                return envelope;
            }