public TreeNode Add(TreeNode node)
 {
     node.Parent = this;
     _children.Add(node);
     return node;
 }
 public bool RemoveChild(TreeNode node)
 {
     return _children.Remove(node);
 }
 public TreeNode Add(string value)
 {
     var node = new TreeNode(value) { Parent = this };
     _children.Add(node);
     return node;
 }