public FirstChildNextSiblingNode(T data, FirstChildNextSiblingNode <T> child, FirstChildNextSiblingNode <T> sibling)
 {
     Data        = data;
     FirstChild  = child;
     NextSibling = sibling;
 }
 public FirstChildNextSiblingTree(FirstChildNextSiblingNode <T> root)
 {
     Root = root;
 }
 public FirstChildNextSiblingNode(T data, FirstChildNextSiblingNode <T> child)
 {
     Data       = data;
     FirstChild = child;
 }