How to save/load an object

public class TaskViewModel : INotifyPropertyChanged
{
    private Task vmTask;    
    private ObservableCollection<TaskViewModel> vmSubTasks;
    TaskViewModel vmParent;
    bool vmIsExpanded;
    bool vmIsSelected;
    public bool VmIsVisited { get; set; }

    //ctors
    public TaskViewModel(Task task, TaskViewModel prnt)
    {
        VmTask = task;  //:Me vmTask = task;
        Parent = prnt; //:Me vmParent = parent; 
        ///<summary>
        ///recursively walks down the Task tree, wrapping each Task object in a TaskViewModel
        ///</summary>
        SubTasks = new ObservableCollection<TaskViewModel>( //:Me vmSubTasks = new ObservableCollection<TaskViewModel>(
                (from t in vmTask.SubTasks
                 select new TaskViewModel(t, this)).ToList<TaskViewModel>());          
    }
    public TaskViewModel(Task task)
        : this(task, null)
    { }
    public bool IsExpanded
    {
        get { return vmIsExpanded; }
        set
        {
            if (value != vmIsExpanded)
            {
                vmIsExpanded = value;
                this.OnPropertyChanged("IsExpanded");
            }
            // Expand all the way up to the root.
            if (vmIsExpanded && vmParent != null)
                Parent.IsExpanded = true;   //fantastic! (executes the setter again)
        }
    }
    public bool IsSelected
    {
        get { return vmIsSelected; }
        set
        {
            if (value != vmIsSelected)
            {
                vmIsSelected = value;
                this.OnPropertyChanged("IsSelected");
                OnPropertyChanged("Name");  //required: reflects the change of txtName to the corresponding TreeViewItem name  
                //OnPropertyChanged is only required for the Name property
            }
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    } 
}