src/main/java/com/basistech/tclre/Compiler.java
private long nfatree(Subre t) throws RegexException {
        assert t != null && t.begin != null;

        if (t.left != null) {
            nfatree(t.left);
        }
        if (t.right != null) {
            nfatree(t.right);
        }
        return nfanode(t);
    }
private long nfatree(Subre t) throws RegexException {
        assert t != null && t.begin != null;

        if (t.left != null) {
            nfatree(t.left);
        }
        if (t.right != null) {
            nfatree(t.right);
        }
        return nfanode(t);
    }
/* optimize results from top node