My thoughts on these cards:
I walk my dog every other day at a cemetery (it's not morbid at all, it's a beautiful place with lots of trees.) In fact, when I need inspiration for trees, I will go there for inspiration! So my mind naturally goes to trees when I think about a sympathy card.
I used Angela's Tree Clinic class to help me paint better trees. these are a fun study that I turned into a card!
Bellow is a youtube tutorial from her class that will help you get started: