Updated insert method to allow items to be added to the end of the list.

C#/Datastructures/DoublyLinkedList.cs

@@ -105,9 +105,12 @@ namespace C_.Datastructures
             }
 
             //Set tail to new item if index is the end
-            if (index == Count)
+            if (index == Count - 1)
             {
+                //Decrement count as it will be be re-incremented once appended
+                Count--;
                 Append(value);
+                return;
             }
 
             //Fetch point in list and add new item

C#/Program.cs

@@ -29,14 +29,15 @@ list.Append(3);
 list.Append(4);
 list.Append(5);
 list.Append(6);
+list.Insert(6, 1);
 
 Console.Write($"{list[0]} ");
 Console.Write($"{list[1]} ");
 Console.Write($"{list[2]} ");
 Console.Write($"{list[3]} ");
 Console.Write($"{list[4]} ");
-Console.Write($"{list[5]} \n");
-Console.Write($"{list[6]} ");
+Console.Write($"{list[5]} ");
+Console.Write($"{list[6]} \n");
 
 
 //DoublyLinkedList<int> list2 = new DoublyLinkedList<int>();