gistfile1.rb

class Node
  attr_reader :children
  attr_reader :value

  def initialize(value)
    @children = []
    @value    = value
  end

  def add_children(*values)
    values.each do |value|
      children << Node.new(value)
    end
  end

  def find_node(value)
    return self if value == self.value
    children.map { |child| child.find_node(value) }.compact.first
  end

  def print_tree
    nodes = [self]
    while nodes.length > 0
      puts    nodes.map { |node| node.value    }.join(' ')
      nodes = nodes.map { |node| node.children }.flatten
    end
  end
end

root = Node.new('A')

root.add_children('B', 'C')
root.find_node('B').add_children('D', 'E')
root.find_node('C').add_children('F', '0', '1')
root.find_node('D').add_children('G', 'H')
root.find_node('G').add_children('I', 'J')
root.find_node('0').add_children('2', '3')

root.print_tree

gistfile2.txt

A
B C
D E F 0 1
G H 2 3
I J