Please can you provide your OE version?
This isn't possible with native OE controls directly. And how will depend on a number of other factors. If you have access to Infragistics controls then there is a TreeView in those libraries. Alternatively I'm sure there are other .Net style libraries you can use.
You could use an OCX, again there are options out there, but please make sure you use an OCX that has a 64bit version as you do not want to build a new 32bit dependency in this day and age.