private void mergeForceCollapse() {
        while (nbRuns > 1) {
            int n = nbRuns - 2;
            if (n > 0 && runsLength[n - 1] < runsLength[n + 1]) {
                n--;
            }
            mergeRuns(n);
        }
    }
Merge all the remaining runs to merge
jme3-core/src/main/java/com/jme3/util/ListSort.java