Prolog Programming -> Binary Tree to list.

Implement the predicate treeToList(X,List), where X is a given ordered non-empty binary tree, and List is an ordered list of elements in nodes of the tree.

Partial Solution Provided:

treeToList(X,List) :- binaryTree(X), convert(X,List).

/* The helping predicate convert(X,List) is true if X is a given non-empty tree, and List is a representation of this tree as an ordered list. */

convert( tree(Element,void,void), List) :- List=[Element]. /* Leaf in a tree */

/* Write the recursive rule and finish the answer */

convert( tree(Root,Left,Right), List) :- ???????????