@Override
	public int size() {
		return isRoot() ? _genes.length() : TreeGene.super.size();
	}
Return the whole flattened tree values in breadth-first order. This method
will always return the same {@code ISeq} instance.

@return the whole flattened tree values
jenetics.ext/src/main/java/io/jenetics/ext/AbstractTreeGene.java