Made this to see how well I could make a material in Cycles for plant matter. Modelled in ngPlant (not based on the Nature Academy, I’ve never seen it), and rendered to 500 passes. Feedback and critique is welcome, the bark was a bit rushed.
Very nice! I’d suggest reshaping the trunk and the lower branches manually; right now one can easily see that that area is made out of multiple separate shapes.
The silhouette of the tree looks really nice and realistic.
The bark texture though looks very boring and uniform, I’d suggest using a texture with much more tonal variance and
give it some displacement.
Also you could make lighting more realistic by using an HDRI map, also the leaves might have some specularity and transparency.
looks good. I think the leaves look especially good, it would be nice if the trunk was a bit more detailed though.
I Agree with other commenters: the leaves look great, the trunk is letting down the leaves. If you spent more time on the bark/trunk it would be great.
I’ve been trying to get that nice, “fluffy” feel to the leaves with the BI; I shall have to try cycles! 
Thanks for the feedback 
This was more of an experiment, hope to do a full nature scene sometime with more detail to the plants. My simple shader for the leaves is here, adding some glossiness sometime would make it look nicer (and slow down the render).
Goldenfrog: You should be able to do the same in BI by tweaking the translucency value of the material or adding SSS. Although, I would use Cycles if you have a recent graphics card, it reduces render times drastically on the GPU with a lot nicer results.