They look like a great start, Rob.
I’ve yet to make my first tree, but perhaps you might permit me to make a couple of suggestions that I’m going to try myself when time permits?
I’d guess they need sealing somehow, and after that maybe dress the tops with thinned-out seafoam to represent the thinner branches found at the ends? A guy did this on a video I saw to enhance plastic armatures to great effect (although it takes time, you can remove the seed-ey bits until you just have thin stems left, which are glued onto the ends with super glue).
In relation to colouring, a light spray of dark grey to the trunk and lower branches, followed by a dark brown to the upper branches makes a great base for the top colours of: raw sienna, yellow ochre and light grey acrylics, mixed with matt medium to provide different shades, which are then dry-brushed onto the trunk and branches.
As I say, just a suggestion, as you will probably have your own (better) ideas in mind to relieve the natural brown of the roots (weathering powders?).
Good luck!
Jonte