import bpy


AREA = 'NODE_EDITOR'

for window in bpy.context.window_manager.windows:
    for area in window.screen.areas:

        if not area.type == AREA:
            continue

        for s in area.spaces:
            if s.type == AREA:
                if len(s.path) == 1:
                    s.path.pop()
                    s.path.append(bpy.data.node_groups['NodeTree'])
                    s.path.append(s.path[0].node_tree)