Well, it looks very photographic, but in fact megascans are 'photo's wrapped around a shape'. In that sense it looks very good, also the mishmash of added stuff. Though if you look carefully some branches repeat themselves a bit obviously, so you might want to edit one or two.
Perhaps the most unsatisfying part would indeed be a clear subject, as you state yourself. A bug or a few bugs (damselfly, dragonfly, or butterfly) would be a good addition. Lots on the web, I think. Perhaps add a very small pool of moisture that would attract them, so you add a story to this scene. Have some sitting, some flying over that little pool of water or wet mud. Nice challenge!
What you also can do is make the arrangement of megascans more satisfying, to add a clear focal attention point, and or use a spotlight to (fake) a lightbeam through canopy lighting out a small area dramatically.
The mentioned small pool would also be a focal point, reflecting some blue sky.
