diff --git a/ch6/Trie.py b/ch6/Trie.py
index bfd0170..dea94eb 100644
--- a/ch6/Trie.py
+++ b/ch6/Trie.py
@@ -1,53 +1,62 @@
-class vertex:
-  def __init__(self, chr: str):
-    self.alphabet = chr
-    self.exist = False
-    self.child = [None] * 26
+def norm_codepoint(s: str, base: int = ord("A")) -> int:
+    """Return integer represening normalized codepoint for a given base."""
+    return ord(s)-base
+
+class Vertex:
+    def __init__(self, ch: str):
+        self.alphabet = ch
+        self.exist = False
+        self.child = [None] * 26
 
 class Trie:
-  def __init__(self):
-    self.root = vertex('!')
-
-  def insert(self, word):
-    cur = self.root
-    for w in word:
-      alphaNum = ord(w)-ord('A')
-      if cur.child[alphaNum] == None:
-        cur.child[alphaNum] = vertex(w)
-      cur = cur.child[alphaNum]
-    cur.exist = True
-
-  def search(self, word):
-    cur = self.root
-    for w in word:
-      alphaNum = ord(w)-ord('A')
-      if cur.child[alphaNum] == None:
-        return False
-      cur = cur.child[alphaNum]
-    return cur.exist
-
-  def startsWith(self, prefix):
-    cur = self.root
-    for w in prefix:
-      alphaNum = ord(w)-ord('A')
-      if cur.child[alphaNum] == None:
-        return False
-      cur = cur.child[alphaNum]
-    return True
-
-
-def main():
-  T = Trie()
-  S = ['CAR', 'CAT', 'RAT']
-  for s in S:
-    print('Insert', s)
-    T.insert(s)
-
-  print('\'CAR\' exist?', T.search("CAR"))
-  print('\'DOG\' exist?', T.search("DOG"))
-  print('Starts with \'CA\' exist?', T.startsWith("CA"))
-  print('Starts with \'Z\' exist?', T.startsWith("Z"))
-  print('Starts with \'AT\' exist?', T.startsWith("AT"))
-
-
-main()
+    def __init__(self):
+        self.root = Vertex("!")
+
+    def insert(self, word: str) -> None:
+        cur = self.root
+        for char in word:
+            alpha_num = norm_codepoint(char)
+            current_child = cur.child[alpha_num]
+            # If current_child is None, set cur as new Vertex instance.
+            cur = current_child or Vertex(char)
+        cur.exist = True
+
+    def search(self, word: str) -> bool:
+        cur = self.root
+        for char in word:
+            alpha_num = norm_codepoint(char)
+            current_child = cur.child[alpha_num]
+            if not current_child:
+                return False
+            cur = current_child
+        return cur.exist
+
+    def starts_with(self, prefix: str) -> bool:
+        cur = self.root
+        for char in prefix:
+            alpha_num = norm_codepoint(char)
+            current_child = cur.child[alpha_num]
+            if not current_child:
+                return False
+            cur = current_child
+        return True
+
+
+if __name__ == "__main__":
+    t = Trie()
+    words = "CAR", "CAT", "RAT"
+    for word in words:
+        print("Inserting: ", word)
+        t.insert(word)
+
+    print()
+
+    prefixes = "CA", "Z", "AT"
+    results = map(t.starts_with, prefixes)
+    for prefix, result in zip(prefixes, results):
+        print(f"""Starts with "{prefix}" exist? {result}""")
+
+    print()
+
+    print(f""""CAR" exist? {t.search(words[0])}""")
+    print(f""""DOG" exist? {t.search("DOG")}""")