Ah Ha! I'm planning a 1/48th scale one, with a FW190A8, for the diorama guide! However, if you're going to do a winter one, then it's much easier, as many items can be obtained from Garden Centres, florists etc. Using real twigs, with a minimum of dressing, 'winter' trees can be made very convincingly, especially those spindly ones, such as silver birch, and some of the conifers. The model railway examples that Wojtek and I mentioned can be enhanced to look very convincing, but the problem there is scale. The largest HO/OO tree can be used for small to medium in 1/32nd, and will be more convincing in 1/48th, where they won't need as much work, but the scale effect becomes more important, in order not to make any foliage or branches look too 'heavy'.
The trees I made and adapted for the Gustav diorama only just get away with it in 1/32nd scale, representing young trees at the edge of the forest/woods; in 1/48th they'd be much better looking,but, these were among the tallest (the adapted ones) available from the HO/OO model railway types, without going to the expense of ridiculous sums per tree, like £5 to £8 !!