How to walk a pivot table?

I have a table 2 students and companies, the relationship is A student can work in many companies and a company can have many students consequently results in a pivot table student_business This pivot table has more independent additional data, when doing the insert in the table it works but how can I go through or visualize the data in this table?

My student model

class Alumno extends Model {
public function empresas()
{
    return $this->belongsToMany(Empresa::class)->withPivot('fechaIncio',
   'fechaConclusion','tipoSupervisor','supervisorNombre','fechaReconocimiento');


}
} 

My business model

class Empresa extends Model{
public function alumnos()
{
    return $this->belongsToMany(Alumno::class)->withPivot('fechaIncio','fechaConclusion',
   'tipoSupervisor','supervisorNombre','fechaReconocimiento');
}
}

I try to do so by accessing a data as follows:

$alumno = App\Alumno::findOrFail(1);
return $alumno->empresa->pivot->fechaIncio;

but generates the following error

  

Trying to get property of non-object