class Tree
    attr_accessor :children, :node_name

    def initialize(hash)
        @children = []
        hash.keys.each { |k|
            @node_name = k
            hash[k].keys.each { |ck|
                @children << Tree.new(hash[k][ck])
            }
        }
    end

    # def initialize(name, hash)
        # @children = []
        # @node_name = name
        # hash[name].keys.each { |k|
            # @children << Tree.new(k, hash[name][k])
        # }
    # end

    def visit_all(&block)
        visit &block
        children.each {|c| c.visit_all &block}
    end

    def visit(&block)
        block.call self
    end
end

x = {"grandpa" => { "dad" => {"child 1" => {}, "child 2" => {} }, "uncle" => {"child 3" => {}, "child 4" => {} } } }
y = Tree.new(x)