enchanted tree saplings

Create a mechanism whereby players can enchant tree saplings. 

Enchanted tree saplings placed adjacent to each-other can grow a tree shape and size that correlates to the number of adjacent tree saplings planted. All sapling types gain the same behavior when enchanted, but only one wood grows in the tree , either all saplings must be the same, or one random sapling of those placed is selected to be the resulting wood. 

Perhaps it is only necessary for one sapling to be enchanted, and then all saplings placed around it must be of one type , and then enchanted saplings can be difficult or rare.