As you can see from the diagram, the white wire is used -- it completes the circuit back to the electrical supply's neutral line. one where the light fixture is between the supply and the switch. I think this is what you mean by a "standard black-white setup". In the parse tree, most of the leaf nodes are single child to their parent nodes. In the syntax tree, we can eliminate this extra information. Syntax tree is a variant of parse tree. In the syntax tree, interior nodes are operators and leaves are operands. Syntax tree is usually used when represent a program in a tree structure.