Add binary search tree.

src/data-structures/tree/BinaryTreeNode.js

@@ -5,12 +5,12 @@ export default class BinaryTreeNode {
     this.value = value;
   }
 
-  addLeft(node) {
+  setLeft(node) {
     this.left = node;
     return this;
   }
 
-  addRight(node) {
+  setRight(node) {
     this.right = node;
     return this;
   }

src/data-structures/tree/__test__/BinaryTreeNode.test.js

@@ -15,8 +15,8 @@ describe('BinaryTreeNode', () => {
     const rootNode = new BinaryTreeNode(2);
 
     rootNode
-      .addLeft(leftNode)
-      .addRight(rightNode);
+      .setLeft(leftNode)
+      .setRight(rightNode);
 
     expect(rootNode.value).toBe(2);
     expect(rootNode.left.value).toBe(1);
@@ -29,8 +29,8 @@ describe('BinaryTreeNode', () => {
     const rootNode = new BinaryTreeNode(2);
 
     rootNode
-      .addLeft(leftNode)
-      .addRight(rightNode);
+      .setLeft(leftNode)
+      .setRight(rightNode);
 
     expect(rootNode.traverseInOrder()).toEqual([1, 2, 3]);
 

src/data-structures/tree/binary-search-tree/BinarySearchTreeNode.js

@@ -2,6 +2,11 @@ import BinaryTreeNode from '../BinaryTreeNode';
 
 export default class BinarySearchTreeNode extends BinaryTreeNode {
   insert(value) {
+    if (this.value === null) {
+      this.value = value;
+      return this;
+    }
+
     if (value < this.value) {
       // Insert to the left.
       if (this.left) {

src/data-structures/tree/binary-search-tree/__test__/BinarySearchTreeNode.test.js

@@ -9,6 +9,15 @@ describe('BinarySearchTreeNode', () => {
     expect(bstNode.right).toBeNull();
   });
 
+  it('should insert in itself if it is empty', () => {
+    const bstNode = new BinarySearchTreeNode();
+    bstNode.insert(1);
+
+    expect(bstNode.value).toBe(1);
+    expect(bstNode.left).toBeNull();
+    expect(bstNode.right).toBeNull();
+  });
+
   it('should insert nodes in correct order', () => {
     const bstNode = new BinarySearchTreeNode(2);
     bstNode.insert(1);