I have a similar situation with my flowers, for example, my rose. For your reference:
https://www.etsy.com/listing/116833210/custom-french-beaded-flower-long-stemmed?ref=shop_home_activePeople can pick color, finish (matte, glossy, pearl, etc), transparency (opaque), color of petals vs color of stem... really, anything can be varied.
I picked ONE variation -- the color of the petals (the color of the rose) and then suggested people to put in the "notes to seller" any other specifications they have. So, I'd suggest maybe one or two variations for people to select, and then explain what else can be changed in the description.
Or, you could set up multiple listings to address one of the variations -- you could list one of each kind of tree, for example, which would not only show customers that you do variation, but also take one of the "options" away from the listing they purchase.
Of course, upon purchase, touching base with the customer to confirm options will clarify things for both of you.