Add doctest for previous fix

Author: furthermares

Diff for: data_structures/trie/radix_tree.py

@@ -59,6 +59,11 @@ def insert(self, word: str) -> None:
             word (str): word to insert
 
         >>> RadixNode("myprefix").insert("mystring")
+
+        >>> root = RadixNode()
+        >>> root.insert_many(['A', 'AA'])
+        >>> root.nodes['A'].nodes['A'].prefix
+        'A'
         """
         # Case 1: If the word is the prefix of the node
         # Solution: We set the current node as leaf