Pointing the camera at the sun is a tricky bit of business. When you consider the old rule on a box of film was to keep the sun over one shoulder... this flies in the face of it and is quite to the contrary.
When the sun is behind your subject, you have to "expose" the camera for the shadows. If the sun is behind your subjects head, his/her face is going to be full shadow. With the sun and the earth, as my 6 year-old son say's, that would be night-night time. The back of your subjects head would be like the other side of the world when it's night on their face. So, this is a case where you have to compromise and burn out the background to expose for the foreground.
However in your shot, you want to capture the effect of the setting sun and how it plays on sky and the trees. If you notice, one of your shots, you can actually see the green of the trees... but the sky is basically blown out. On that one you exposed for the trees. Not what we want here.
What we really need to capture the excitment of the sky ... which is what you saw when you were standing there is to go ahead and expose correctly for the sky.. and let the trees be damned. This would be a silhouette.
The camera can't truly record what you actually see in this situation. You're eyes are dynamic and continually adjusting. This is the fun of photography. We now have to trick the camera and control its capabilities AND limits to compose or report the story we want to tell.
So, you might have waited and let the trees mask the camera from the sun... let it get a little lower and then expose for the sky.... maybe even under expose to add more drama.
Think about when sunset REALLY gets cool... it's after the sun goes down. That's when the sky goes really nuts and explodes with color... it's after sundown and at twilight.
Here are a couple of examples I shot last night. These four were within a 25 minute period. I did these on a tripod and kept the ISO down at 100 and shot RAW.
I leave all the EXIF data intact in my images. If you're using FireFox, download the EXIF viewer plug in. It will reveal the settings.