diff --git a/WanaKanaShaapu.UnitTest/ToKanaUnitTests.cs b/WanaKanaShaapu.UnitTest/ToKanaUnitTests.cs
index 615e8f0..4f123d6 100644
--- a/WanaKanaShaapu.UnitTest/ToKanaUnitTests.cs
+++ b/WanaKanaShaapu.UnitTest/ToKanaUnitTests.cs
@@ -19,6 +19,7 @@ public void ToKana_WhenPassedAnEmptyString_ReturnsAnEmptyString(string input, st
         [TestCase("chyx", "chyx")]
         [TestCase("shyp", "shyp")]
         [TestCase("ltsb", "ltsb")]
+        [TestCase("chuu", "ちゅう")]
         public void ToKana_WhenPassedInput_ConvertsItCorrectly(string input, string expectedOutput)
         {
             string result = WanaKana.ToKana(input);
diff --git a/WanaKanaShaapu/TreeBuilder.cs b/WanaKanaShaapu/TreeBuilder.cs
index f9596e0..81adf90 100644
--- a/WanaKanaShaapu/TreeBuilder.cs
+++ b/WanaKanaShaapu/TreeBuilder.cs
@@ -25,19 +25,19 @@ private static void AddToTree(Dictionary<string, Node> tree, (string Romaji, str
 
         private static void AddNode(Node node, string romaji, string kana)
         {
-            if (romaji.Length == 1 && !node.Children.ContainsKey(romaji))
+            if (romaji.Length == 0)
+                return;
+            else if (romaji.Length == 1 && !node.Children.ContainsKey(romaji))
                 node.Children.Add(romaji, new Node(kana));
             else if (romaji.Length == 1 && node.Children.ContainsKey(romaji))
                 node.Children[romaji].Data = kana;
             else
             {
-                foreach (char c in romaji)
-                {
-                    if (!node.Children.ContainsKey(c.ToString()))
-                        node.Children.Add(c.ToString(), new Node(string.Empty));
-                    node = node.Children[c.ToString()];
-                    AddNode(node, romaji[1..], kana);
-                }
+                var firstChar = romaji.First().ToString();
+                if (!node.Children.ContainsKey(firstChar))
+                    node.Children.Add(firstChar.First().ToString(), new Node(string.Empty));
+                node = node.Children[firstChar.ToString()];
+                AddNode(node, romaji[1..], kana);
             }
         }