how can i create further sub context menu in theia file explorer
have you seen our documentation on menu items yet? I would recommend you to look into it and come back if you have more specific questions about any issues you have encountered on the way.
Just to expand on what Mark said, the menu paths for the navigator (explorer) context-menu are defined as:
You’ll want to create a submenu path for your submenu using one of the above paths (this will add it to the navigator context-menu).
Then, the idea is (using the path you specified above), to simply register your
registerSubMenu then register your command to that
We have many examples already in the codebase about submenus that should help, including our api-samples (https://github.com/eclipse-theia/theia/blob/master/examples/api-samples/src/browser/menu/sample-menu-contribution.ts). The main difference is the path in which you want to add your menu item.