This is my contribution so far. I'm not sure if it is complete yet and would welcome feedback :)
I drew the initial tree study in situe in your book Katie. This is a bit unnerving in case it got muddy or had some other accident!
The tree is an amazing Crack Willow and shows a wonderful record of its life in colour and texture.
I have kept the colour quite restained and haven't yet decided whether to add colour between the trees.