Dispose a form having user control

Hi,,,

  I have created a windows application using c#. I have included a user control, which has tree view. I have included this user control in all forms.

My issue is : As the tree view is in all forms, when i try to show a second form, the first form is also visible, moreover the second form appears below the first form. I tried to dispose the first form,when the second form loads, but its disposing only the user control and not the first form.

  Please help me in disposing the first form, and making only one form active and visible at one point of time. The first form should not be running at the backend. It should be disposed.

Please help