Found in SDK Help type Merge and the first on is right one 🙂
Type: Command
Caption: Merge
Name: Editor_Merge
Command: Editor
Category GUID (CLSID / ProgID): {DB56FE71-F74D-11D1-849A-0000F875B9C6} esriEditor.MergeCommand
Sub Type: none
Parent: Editor_EditorMenu
Description: Merges the selected features