Show calendar on custom DateTimePicker

Question

I created a custom datetimepicker based on the UserControl in Visual Studio 2010 c#. There are a RichTextBox, a Button and MonthCalendar in this control.

https://i.stack.imgur.com/zT8Lw.png.

I change height of the UserControl to hide/show calendar. My problem is that when I place this control on the GroupBox which is located on the panel, parent overlaps it:

https://i.stack.imgur.com/JQMuo.png

I've solved this looping back on controls Parent until the main form is found and then setting it as parent of my DateTimePicker.

    Control parent = this.Parent ?? null;
        while (parent != null)
        {
            if (parent is Form)
                break;
            parent = parent.Parent;

        }
        this.clnMonth.Parent = parent;
        clnMonth.Location = this.PointToScreen(Point.Empty);

I've tried to place MonthCalendar on another form and show/hide it after click, but there where huge problem positioning the form under the DateTimePicker. The above method works fine, but I know it's not the best solution. Could you give me any alternative idea?