nested entities / list nested in Doctrine

I have two Plates and Candidate tables with the same structure:

TABLE Chapa (
    id INT AUTO_INCREMENT NOT NULL,
    PRIMARY KEY(id)
)
TABLE Candidato (
    id INT AUTO_INCREMENT NOT NULL,
    chapa_id INT DEFAULT NULL,
    PRIMARY KEY(id)
)

And the respective entities:

<?php
use Doctrine\Common\Collections\ArrayCollection;

/** @Entity */
class Chapa
{
    // ...
    /**
     * Uma Chapa possui Muitos Candidatos.
     * @OneToMany(targetEntity="Candidato", mappedBy="chapa")
     */
    private $candidatos;
    // ...

    public function __construct() {
        $this->candidatos = new ArrayCollection();
    }
}

/** @Entity */
class Candidato
{
    // ...
    /**
     * Muitos Candidaatos possuem Uma Chapa.
     * @ManyToOne(targetEntity="Chapa", inversedBy="candidatos")
     * @JoinColumn(name="chapa_id", referencedColumnName="id")
     */
    private $chapa;
    // ...
}

With the following queryBuilder I get the result:

$qb = $this->createQueryBuilder('ch')
           ->select('ch.numero, cds.nome' )
           ->leftJoin('ch.candidatos', 'cds')
           ->getQuery()
           ->getResult();

// Resultado
{
  "data": [
    {
      "numero": "Chapa 10",
      "nome": "Candidato 1"
    },
    {
      "numero": "Chapa 10",
      "nome": "Candidato 2"
    }
  ],
  "success": true
}

How do I get the following result (nested)?

{
  "data": [
    {
      "numero": "Chapa 10",
      "candidatos": [
        {
          "nome": "Candidato 1"
        },
        {    
          "nome": "Candidato 2"
        }
      ]
    }
  ],
  "success": true
}