importing and updating the .fbx file in unity

I already have the .fbx file of my mesh model of my game map and also able to import it in unity. The problem is that, I open the .blend file again and append an object to the existing mesh model of the map and export it again as .fbx file, it seems that the appended object is not appearing in unity but the name of the file is there. What do you think is the problem here?