c# create xml from byte array

Assuming your xml is in the default 'UTF8' encoding., you could do something like this;

string xml = System.Text.UTF8Encoding.UTF8.GetString(bytes);
System.Xml.XmlDocument xdoc = new System.Xml.XmlDocument().LoadXml(xml);

Or this;

XmlDocument doc = new XmlDocument();
using (MemoryStream ms = new MemoryStream(buffer))
{
    doc.Load(ms);
}