XML document append child and escape special characters

I am facing this specific scenario where my escape sequences are getting replaced twice.

I have a code similar placed similar as below:

XmlDocument xmldoc=new XmlDocument();

XmlNode root=xmldoc.CreateElement("root");

XmlNode node=xmldoc.CreateElement("test");

string str="This is \"Country's\" & nations challenge";

//All escape sequences are removed.Below finctions correctly and replaces all special characters

node.InnerText= System.Security.SecurityElement.Escape(str);

//This will again replace and only & with & is anything wrong here? so text " will be replaced with &qout

root.AppendChild(node);

I tried  it by giving  node.Innertext=str; just to avoid double replacement but it seems appendchild only replaces & with an &

Is there a proper way to resolve this issue?