Add binary search tree.

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

@@ -13,7 +13,27 @@ export default class BinarySearchTree {
     return this.root.contains(value);
   }
 
+  remove(value) {
+    const nodeToRemove = this.findNode(value);
+
+    if (!nodeToRemove) {
+      throw new Error('Item not found in the tree');
+    }
+
+    if (!nodeToRemove.left && !nodeToRemove.right) {
+      // Node is a leaf and thus has no children.
+      // Just remove the pointer to this node from the parent node.
+    } else if (nodeToRemove.left && nodeToRemove.right) {
+      // Node has two children.
+      // Find the next biggest value (minimum value in the right branch)
+      // and replace current value node with that next biggest value.
+    } else {
+      // Node has only one child.
+      // Make this child to be a direct child of current node's parent.
+    }
+  }
+
   toString() {
-    this.root.toString();
+    return this.root.toString();
   }
 }