Several classical schemes exist to represent trees as strings over a fixed alphabet; these are useful in many algorithmic and conceptual studies. Our previous work has proposed a representation of unranked trees as strings over a countable alphabet, and has shown how this representation is useful for canonizing unordered trees and for mining closed frequent trees, whether ordered or unordered. Here we propose a similar, simpler alternative and adapt some basic algorithmics to it; then we show empirical evidence of the usefulness of this representation for mining frequent closed unordered trees on real-life data.