Patience H, that's the secret of modelling. Speed = s*it. Patience = good. It's not a race to get it finished, it's a hobby to absorb, and end up with a good, hopefully very good, result.
Andy, there's a few ways I use, some of which are shown (I think!) in Part One of my Diorama Guide, and some in the Gustav thread from about a year ago. This time around, I'll be making mainly Silver Birch, with a couple of Beech or similar. I'll be using various gauges of wire, twisted into armatures, then either tape wrapped and/ or some filler or putty. Folliage will be a mix of (possibly Sea Moss) a small basis of lichen, with some local (like Woodland Scenics) tree foliage material, and additions such as dried herbs and tea leaves etc., and if I can remember the name, or find it at the local garden centre, a type of fern which, when properly selected and mixed in, looks the biz.
This part of the build will be forming an unfinished section of the (eventually) forthcoming Part Two of the diorama guide - it's only a year late!!
BTW, in case you can't find it, here's what the 'quick' trees looked like in the Gustav thread, in 1/32nd scale.