Another stellar piece! I really love the scene you created here. You said the tree took a lot of time to do, and your effort has not been wasted. It's very fantasy-looking with the purple leaves and twisted tree trunk. The grass is also pretty classy looking (and do I really need to say anything about the water after the last critique I wrote XP )
The unicorn is beautiful. I can tell he (or she?) has glossy fur and hair. He's obviously magical too, as evidenced by the glow cast on the leaves by his horn. I think the magic effect is a tad lost in the bright colors though, especially with the horn being so thin. If you had beefed up the horn or somehow emphasized its separate-ness from the glowing leaves around it, the effect would have been nicer.
I think you also made the unicorn's mane and tail a bit too glossy-looking. They might need to be a tad darker. Currently, I find them a bit too distracting (I noticed how glossy the mane and tail were way before I noticed the unicorn had a glowing horn).
Other than those two critiques, I think you a did a marvelous job with this piece. You have excellent pixel skills.
Your detail and anatomy are absolutely stunning! I love the shading on this one, and once again it's amazing how quick you draw such things! Loving the way you've drawn the tree trunk, looks almost fantasy-like. Very pretty! (I actually think this is deserving of a DD : ) )