Append to existing XML doesnt work Unity3D

I am currently trying to make a save storage system in Unity3D. For this I load and save all necessary data. But if I save again it overwrites the xml file. And when I use append it adds the xml root twice, which means that I cannot load the xml structure. How can I only add the necessary data when saving the xml data without duplicating the root?

![alt text][1]

ActorContainer should one exist one time.

![alt text][2]

Hope someone can help me.. [1]: /storage/temp/174635-one.png [2]: /storage/temp/174636-two.png