BuyDebug. I assume you know how to enable BuyDebug? If not:
1. Press Ctrl+Shift+C to open the cheats panel.
2. Type "testingcheatsenabled true" without quotations.
3. Press enter.
4. Press Ctrl+Shift+C to open the cheats panel.
5. Type "BuyDebug On".
6. Press Enter.
In Buy Mode a "?" category will open up. Click on the seeds tab. Choose your plant, and place it. If you don't get a tree to your liking (Ready to harvest, if you want Mature), place it and keep placing trees until you have the desired amount of trees, then simply delete the rest.
I think you know how to enable BuyDebug, but I had to cover all bases.