1. A remove option after placing the tree, i know you can just chop it down like normal but maybe a quick remove option whether it's holding E to pick up, or a command. That can be down to you I guess, as some players like to place their trees in a specific position and with this remove option this will speed things up when base building, and of course the tree/sapling will be refunded to the inventory but the currency will not. Maybe add in a setting where players will get charged a small free for quickly removing the tree using their currency type.
2. Using economics/custom currency to buy trees is good but for my server i use custom currency which is still linked to economics but i have to place the custom cash inside my inventory to be able to buy a tree when it would be nice to just take it straight out of my cash virtually. I tried this with just the economics setting on true but as i have custom currency this didn't work. So maybe have a look in to this too if you can.
3. add a search option as there are a lot of trees in this UI