C＃app应该是异步的，但UI仍然会冻结

I have created a small C# application that should pull all values from an XML file asynchronously. The problem is.. it's not asynchronous and I can't see where I'm going wrong. When the button is clicked the UI freezes, the application can't be moved etc, showing all the signs of it running synchronously.I have created a small C# application that shou