diff --git a/source_code/intersection_trees/intersection_tree.py b/source_code/intersection_trees/intersection_tree.py
index 6765f98..6b56d7e 100644
--- a/source_code/intersection_trees/intersection_tree.py
+++ b/source_code/intersection_trees/intersection_tree.py
@@ -66,16 +66,27 @@ def insert(self, interval: Interval) -> None:
         if interval[0] >= interval[1]:
             raise ValueError(f"Invalid interval: start ({interval[0]}) must be less than end ({interval[1]})")
             
+        self._insert(interval)
+
+    def _insert(self, interval: Interval) -> None:
+        '''Private method to insert a new interval [start, end) in the tree.
+        Does not validate the interval.
+
+        Parameters
+        ----------
+        interval: Interval
+            the interval to insert (assumed to be valid)
+        '''
         if interval[0] < self._start:
             if self._left is None:
                 self._left = Node(interval)
             else:
-                self._left.insert(interval)
+                self._left._insert(interval)
         else:
             if self._right is None:
                 self._right = Node(interval)
             else:
-                self._right.insert(interval)
+                self._right._insert(interval)
         self._max_end = max(self._max_end, interval[1])
 
     def search(self, interval: Interval, results: list[Interval]) -> None:
@@ -88,13 +99,34 @@ def search(self, interval: Interval, results: list[Interval]) -> None:
             the interval to search for intersections
         results: list[Interval]
             list to append the results to
+            
+        Raises
+        ------
+        ValueError
+            if interval start is not less than end
+        '''
+        if interval[0] >= interval[1]:
+            raise ValueError(f"Invalid interval: start ({interval[0]}) must be less than end ({interval[1]})")
+            
+        self._search(interval, results)
+
+    def _search(self, interval: Interval, results: list[Interval]) -> None:
+        '''Private method to search for all intervals in the tree that intersect with [start, end)
+        and append them to results. Does not validate the interval.
+
+        Parameters
+        ----------
+        interval: Interval
+            the interval to search for intersections (assumed to be valid)
+        results: list[Interval]
+            list to append the results to
         '''
         if self._start < interval[1] and interval[0] < self._end:
             results.append((self._start, self._end))
         if self._left is not None and self._left._max_end >= interval[0]:
-            self._left.search(interval, results)
+            self._left._search(interval, results)
         if self._right is not None and self._right._max_end >= interval[0]:
-            self._right.search(interval, results)
+            self._right._search(interval, results)
 
     def to_str(self, prefix: str = '') -> str:
         '''Return a string representation of the tree.