Update tree examples to use << insertion shorthand

Switch Trie, AATree, and BTree examples to demonstrate << insertion syntax.\n\nKeep FenwickTree and SegmentTree examples on explicit indexed update semantics, consistent with their documented API design.

Author: evolve75

examples/example_aa_tree.rb

@@ -51,8 +51,8 @@
 
 # Create a tree with the root and its direct children.
 tree = Tree::AATree.new([[30, 'thirty'], [20, 'twenty'], [40, 'forty']])
-# Insert the right child under 20 to match the structure.
-tree.insert(25, 'twenty-five')
+# Insert the right child under 20 using the shovel shorthand.
+tree << [25, 'twenty-five']
 
 # Traverse keys in sorted order.
 puts "keys: #{tree.keys.inspect}"

examples/example_b_tree.rb

@@ -50,28 +50,18 @@
 # Create an empty B-tree with minimum degree 2.
 tree = Tree::BTree.new(2)
 
-# Insert the root entries.
-tree.insert(10, 'ten')
-# Insert the next root entry.
-tree.insert(20, 'twenty')
-# Insert the next root entry.
-tree.insert(30, 'thirty')
-# Insert values that will populate the left child.
-tree.insert(1, 'one')
-# Insert values that will populate the left child.
-tree.insert(5, 'five')
-# Insert values that will populate the second child.
-tree.insert(12, 'twelve')
-# Insert values that will populate the second child.
-tree.insert(18, 'eighteen')
-# Insert values that will populate the third child.
-tree.insert(22, 'twenty-two')
-# Insert values that will populate the third child.
-tree.insert(26, 'twenty-six')
-# Insert values that will populate the fourth child.
-tree.insert(35, 'thirty-five')
-# Insert values that will populate the fourth child.
-tree.insert(40, 'forty')
+# Insert entries using the shovel shorthand.
+tree << [10, 'ten']
+tree << [20, 'twenty']
+tree << [30, 'thirty']
+tree << [1, 'one']
+tree << [5, 'five']
+tree << [12, 'twelve']
+tree << [18, 'eighteen']
+tree << [22, 'twenty-two']
+tree << [26, 'twenty-six']
+tree << [35, 'thirty-five']
+tree << [40, 'forty']
 
 # Traverse keys in order.
 puts "keys: #{tree.keys.inspect}"
@@ -80,7 +70,7 @@
 puts "search 22: #{tree.search(22)}"
 
 # Insert a new key/value pair.
-tree.insert(28, 'twenty-eight')
+tree << [28, 'twenty-eight']
 # Show keys after insertion.
 puts "after insert keys: #{tree.keys.inspect}"
 

examples/example_trie.rb

@@ -52,10 +52,9 @@
 
 # Create the root node.
 root = Tree::TrieNode.new('')
-# Insert the word that builds the c-a-t path.
-root.insert('cat')
-# Insert the single-letter word for d.
-root.insert('d')
+# Insert words with the natural shovel syntax.
+root << 'cat'
+root << 'd'
 
 # Check if a word exists.
 puts "include? cat: #{root.include?('cat')}"