Address comments.

Author: gabi-250

src/lib.rs

@@ -79,7 +79,7 @@ impl<'a, T> SearchTree<T>
     /// assert!(tree.contains(&String::from("world!")));
     /// ```
     pub fn insert(&mut self, value: T) {
-        if let Ok(node) = self.create_node(value) {
+        if let Some(node) = self.create_node(value) {
             self.nodes.push(node);
             // inserted the root
             if self.nodes.len() == 1 {
@@ -121,20 +121,21 @@ impl<'a, T> SearchTree<T>
         Err(previous_index)
     }
 
-    fn create_node(&mut self, value: T) -> Result<Node<T>, usize> {
+    fn create_node(&mut self, value: T) -> Option<Node<T>> {
         match self.get_node(&value) {
-            Ok(index) => Err(index),
-            Err(previous_index) => {
-                if let Some(parent) = previous_index {
-                    if self.nodes[parent].value < value {
-                        self.nodes[parent].right_child = Some(self.nodes.len());
+            Ok(_) => None, // a node containing `value` already exists
+            Err(parent) => {
+                if let Some(parent_index) = parent {
+                    if self.nodes[parent_index].value < value {
+                        self.nodes[parent_index].right_child =
+                            Some(self.nodes.len());
                     } else {
-                        self.nodes[parent].left_child = Some(self.nodes.len());
+                        self.nodes[parent_index].left_child = Some(self.nodes.len());
                     }
                 }
-                Ok(Node {
+                Some(Node {
                     value: value,
-                    parent: previous_index,
+                    parent: parent,
                     left_child: None,
                     right_child: None,
                     height: 0