diff --git a/lectures/18_trees_I/ds_set_starter.h b/lectures/18_trees_I/ds_set_starter.h
index 91117cb..b4fea8e 100644
--- a/lectures/18_trees_I/ds_set_starter.h
+++ b/lectures/18_trees_I/ds_set_starter.h
@@ -1,79 +1,73 @@
-// Partial implementation of binary-tree based set class similar to std::set.  
-// The iterator increment & decrement operations have been omitted.
-#ifndef ds_set_h_
-#define ds_set_h_
-#include <iostream>
-#include <utility>
-
-// -------------------------------------------------------------------
-// TREE NODE CLASS 
 template <class T>
 class TreeNode {
 public:
-  TreeNode() : left(NULL), right(NULL) {}
-  TreeNode(const T& init) : value(init), left(NULL), right(NULL) {}
-  T value;
-  TreeNode* left;
-  TreeNode* right;
+	T key;
+	TreeNode* left;
+	TreeNode* right;
+	// constructor
+	TreeNode(const T& k) {
+		key = k; 
+		left = NULL;
+		right = NULL;
+	}
 };
 
-template <class T> class ds_set;
-
-// -------------------------------------------------------------------
-// TREE NODE ITERATOR CLASS
-template <class T>
-class tree_iterator {
-public:
-  tree_iterator() : ptr_(NULL) {}
-  tree_iterator(TreeNode<T>* p) : ptr_(p) {}
-  tree_iterator(const tree_iterator& old) : ptr_(old.ptr_) {}
-  ~tree_iterator() {}
-  tree_iterator& operator=(const tree_iterator& old) { ptr_ = old.ptr_;  return *this; }
-  // operator* gives constant access to the value at the pointer
-  const T& operator*() const { return ptr_->value; }
-  // comparison operators are straightforward
-  bool operator==(const tree_iterator& r) { return ptr_ == r.ptr_; }
-  bool operator!=(const tree_iterator& r) { return ptr_ != r.ptr_; }
-
-private:
-  // representation
-  TreeNode<T>* ptr_;
-};
-
-// -------------------------------------------------------------------
-// DS SET CLASS
+// internally it's a binary search tree
 template <class T>
 class ds_set {
 public:
-  ds_set() : root_(NULL), size_(0) {}
-  ds_set(const ds_set<T>& old) : size_(old.size_) { 
-    root_ = this->copy_tree(old.root_); }
-  ~ds_set() { this->destroy_tree(root_);  root_ = NULL; }
-  ds_set& operator=(const ds_set<T>& old) {
-    if (&old != this) {
-      this->destroy_tree(root_);
-      root_ = this->copy_tree(old.root_);
-      size_ = old.size_;
-    }
-    return *this;
-  }
-
-  typedef tree_iterator<T> iterator;
-  iterator find(const T& key_value) { return find(key_value, root_); }
-  std::pair< iterator, bool > insert(T const& key_value) { return insert(key_value, root_); }
-  // ITERATORS
-  iterator begin() const { 
-  }
-
-  iterator end() const { return iterator(NULL); }
-
-private:
-  // REPRESENTATION
-  TreeNode<T>* root_;
-  int size_;
-  iterator find(const T& key_value, TreeNode<T>* p) { /* to be implemented */ }
-  std::pair<iterator,bool> insert(const T& key_value, TreeNode<T>*& p) { /* to be implemented */ }
-  void destroy_tree(TreeNode<T>* p) { /* to be implemented */ }
+	ds_set(){
+		root = NULL;
+		m_size = 0;
+	}
+	int size() { return m_size; }
+	bool find(const T& key){
+		return find(key, root);
+	}
+	void insert(const T& key){ 
+		if(insert(key, root)  == true){
+			++m_size;
+		}
+	}
+private: 
+	TreeNode<T>* root;
+	int m_size;
+	bool find(const T& key, TreeNode<T>* root);
+	bool insert(const T& key, TreeNode<T>*& root);
 };
 
-#endif
+template <class T>
+bool ds_set<T>::find(const T& key, TreeNode<T>* root){
+	// base case (if root doesn't even exist)
+	if(root == NULL){
+		return false;
+	}
+	
+	// general case
+	if(key < root->key){
+		return find(key, root->left);
+	}else if(key > root->key){
+		return find(key, root->right);
+	}else{
+		return true;
+	}
+}
+
+template <class T>
+bool ds_set<T>::insert(const T& key, TreeNode<T>*& root){
+	// base case (if root doesn't even exist)
+	if(root == NULL){
+		// make the first node.
+		root = new TreeNode<T>(key);
+		return true;
+	}
+	
+	// general case
+	if(key < root->key){
+		return insert(key, root->left);
+	}else if(key > root->key){
+		return insert(key, root->right);
+	}else{
+		return false;
+	}
+}