class Tree
	attr_accessor :root, :data, :children
		def initialize(parent = nil,data=nil)
			@parent = parent
			@data = data
			@children = []
		end
		def add_subtree(subtree)
			subtree.parent = self
			children.push(subtree)
		end

		def add_node(data)
			children.push(Tree.new(self,data))
		end

		def root?()
			return  not parent.nil?
		end

		def to_a
			return @children.map{|t| t.to_a}
		end

		def walk
		end

		def prune(subtree)
			i = @children.index(subtree)
			if i then
				st = @children[i]
				@children = [0..(i-1)] + [(i+1)..-1]
			end
		end

		def leaf?()
			return @children.empty?
		end
	end