data.cs

public class TrackedChangeModel
{
    public string DocumentName { get; set; }
    public DateTime FirstChange { get; set; } = DateTime.MaxValue;
    public List<TrackedChange> TrackedChanges { get; set; } = new List<TrackedChange>();
}

public class TrackedChange
{
    public string UserName { get; set; }
    public DateTime ChangeTime { get; set; }
    public string Text { get; set; }
    public string HighlightColor { get; set; }
    public ChangeKind ChangeKind { get; set; }
    public string Image { get; set; }
}

public enum ChangeKind
{
    InsertedText = 4096,
    DeletedText = 8192
}