private void Expand()
{
if (this.Type == DirectoryType.File)
{
return;
}
List <DirectoryItem> items = DirectoryStructure.GetDirectoryFolders(this.FullPath);
Children = new ObservableCollection <DirectoryItemViewModel>(items.Select(x => new DirectoryItemViewModel(x.FullPath, x.Type, x.Name, x.Hidden)));
}