The drive letter context menu is controlled by the registry sub-keys keys and Value Names at:
If you wanted to add a Tree menu item, you could:
1. Copy / Paste the following to a DTree.reg file:
Windows Registry Editor Version 5.00
@="cmd.exe /k Tree %L |MORE"
2. Merge the DTree.reg file with your registry, or run regedit /s DTree.reg.