How to persist entities when one has two parents - symfony

Question

Here's my situation:
Framework Symfony 4, using Doctrine(version).
I have three entities : A, B and C.
Entity A has a OneToMany relationship with B, and a OneToMany relationship with C.
Entity B has a OneToMany relationship with C.
In a form, I have a collectionForm about entity C embedded in a collectionForm about entity B.
Adding entities B & C is optional in the form.
However, when trying to add entity C (and therefore entity B), seeing as entity C has two parents (A & B), doctrine fails to know in which order to persist those, and gives the following error :
A new entity was found through the relationship 'App\Entity\EntityC#entityB' that was not configured to cascade persist operations for entity: App\Entity\EntityB#0000000010cd7f460000000077359844. To solve this issue: Either explicitly call EntityManager#persist() on this unknown entity or configure cascade persist this association in the mapping for example #ManyToOne(..,cascade={"persist"}). If you cannot find out which entity causes the problem implement 'App\Entity\EntityB#__toString()' to get a clue.
How do I tell doctrine to persist entity A first, then B and then C in this case ?
So far, I've tried removing the OneToMany relationship between B and C, without any luck, and adding a ManyToOne relationship in entityC for entity B.
I feel if I could bypass this relationship between B and C this could work, but I don't know how.
EntityA :
class entityA extends BaseEntityA {
/**
* #ORM\OneToMany(targetEntity="App\Entity\EntityB", mappedBy="entityA", cascade={"persist"})
* #ORM\JoinColumn(name="id", referencedColumnName="entityA_id", nullable=false)
*/
protected $entitiesB;
/**
* #ORM\OneToMany(targetEntity="App\Entity\EntityC", mappedBy="entityA", cascade={"persist"})
* #ORM\JoinColumn(name="id", referencedColumnName="entityA_id", nullable=false)
*/
protected $entitesC;
...
/**
* Add EntityB entity to collection (one to many).
*
* #param \App\Entity\EntityB $entityB
*
* #return \App\Entity\EntityA
*/
public function addEntityB(\App\Entity\EntityB $entityB)
{
$this->entitiesB[] = $entityB;
$entityB->setEntityA($this);
return $this;
}
/**
* Add EntityC entity to collection (one to many).
*
* #param \App\Entity\EntityC $entityC
*
* #return \App\Entity\EntityA
*/
public function addEntityC(\App\Entity\EntityC $entityC)
{
$this->entitiesC[] = $entityC;
$vehicle->setEntityA($this);
return $this;
}
Entity B :
class EntityB extends BaseEntityB {
/**
* #ORM\OneToMany(targetEntity="App\Entity\EntityC", mappedBy="entityB", cascade={"persist"})
* #ORM\JoinColumn(name="id", referencedColumnName="entityB_id", nullable=false)
*/
protected $entitiesC;
...
/**
* #param Collection $entitiesC
*
* #return $this
*/
public function setEntityC(Collection $entitiesC)
{
$this->entitiesC = $entitiesC;
return $this;
}
/**
* Add EntityC entity to collection (one to many).
*
* #param \App\Entity\EntityC $entityC
*
* #return \App\Entity\EntityB
*/
public function addEntityC(\App\Entity\EntityC $entityC)
{
$this->entitiesC[] = $entityC;
$entityC->setEntityB($this);
$entityC->setEntityA($this->getEntityA());
// Things I tried to remove the relationship between B and C
// $this->getEntityA()->addEntityC($entityC);
// $entityC->setEntityB($this);
return $this;
}
Entity C :
class EntityC extends BaseEntityC {
// Somtehing I tried at some point
// /**
// * #ORM\ManyToOne(targetEntity="EntityB", inversedBy="entitiesC", cascade={"persist"})
// * #ORM\JoinColumn(name="entityB_id", referencedColumnName="id")
// */
// protected $entityB;
...
}
I would like to persist this entities in the right order (A then B then C), using only one form if possible.