C# insert new tag using xelements

the quick <bold>brown</bold> fox jump over the lazy dog. The house full of excitement. The blue car is very nice

the quick <bold>brown</bold> fox <action>jump</action> over the lazy dog. The house full of excitement. The blue car is very nice

private  void GetPreText(IEnumerable<xelement> innodLevels, string _id, ref string innodeLevelValue, ref string tagUsed)
        {
            string pre = string.Empty;
            foreach (var innod in innodLevels)
            {
                string id = innod.Attributes(innod.GetDefaultNamespace() + "id").FirstOrDefault().Value;
                
                if (_id == id)
                {
                    innodeLevelValue = innod.ToString();
                    if (innod.Descendants(innod.GetDefaultNamespace() + "pre").FirstOrDefault().Value == null)
                    {
                        pre = innod.Descendants(innod.GetDefaultNamespace() + "table").FirstOrDefault().Value;
                        tagUsed = "";
			//i need to insert the tag here using the pre variable content
                    }
                    else
                    {
                        pre = innod.Descendants(innod.GetDefaultNamespace() + "pre").FirstOrDefault().Value;
			//i need to insert the tag here using the pre variable content


                    }
                    
                    break;
                }
            }

        }<table></table>