One of the side effects of HDR, is that the processing can add noise, as it is pushing the exposure in some areas. It is particualrly noticeable if you shoot a silhouette. To be honest, I don't really see the need for HDR when shooting a silhouette, as you would normally just expose for the background and leave the foreground completely blocked out. Also, with such large contrast differences in the transition areas, HDR results in unsightly haloes.
You know, posts like that "usually" upset me, as in "dont do what you are trying to do"!
But I took your advice and from a single shot I managed to achieve what I wanted without any HDR at all,
just with the normal tools in Lightroom. So obviously I'm not upset.
And here's the result. Biggest difference is the almost complete lack of noise and Halo around the tree.
I had 5 bracketed shots so basically went the HDR route without trying alternatives first.
Thanks very much for the idea.