ActionHistory_V1 singleton pattern

ActionHistory_V1.cs

public class ActionHistory_V1 : IActionHistory
{
    private Stack<string> _history { get; set; }

    public ActionHistory_V1()
    {
        if (File.Exists("actions.txt"))
        {
            var lines = File.ReadAllLines("actions.txt");

            _history = new Stack<string>(lines.ToList());
        }
        else
            _history = new Stack<string>();
    }
    public void AddAction(string action)
    {
        _history.Push(action);
    }
    public void Save()
    {
        File.WriteAllLines("actions.txt", _history);
    }
    public string RetriveLastAction()
    {
        return _history.FirstOrDefault();
    }
    public List<string> RetriveAllActions()
    {
        return _history.ToList();
    }
}