caMap := make(CertificateTree)

	for _, cert := range m {
		if cert.CAName == "" {
			if _, ok := caMap[cert]; !ok {
				caMap[cert] = []*KubeadmCert{}
			}
		} else {
			ca, ok := m[cert.CAName]
			if !ok {
				return nil, errors.Errorf("certificate %q references unknown CA %q", cert.Name, cert.CAName)
			}
			caMap[ca] = append(caMap[ca], cert)
		}
	}