def prune(nodes)
      nodes.each do |node|
        node.parent.children.reject!{|n| n == node} if (node != @root) && (node.diff_score < @score_threshold)
      end
    end
def prune(nodes)
      nodes.each do |node|
        node.parent.children.reject!{|n| n == node} if (node != @root) && (node.diff_score < @score_threshold)
      end
    end
prune away nodes that don't meet the configured score threshold