`BinTree` is a type. There are two kinds of BinTrees. There are `leaf` BinTrees and there are `node` BinTrees. A leaf has no fields. A node has three fields. Th

`BinTree` is a type. There are two kinds of BinTrees. There are `leaf` BinTrees and there are `node` BinTrees. A leaf has no fields. A node has three fields. Thus, here are some BinTrees: leaf node(1, leaf, leaf) node(2, leaf, node(1, leaf, leaf)) and so on.