Proposal aggregate root relationship with Comment entity

Proposal.cs

public class Proposal
{
    private List<Comments> _comments;
    public ReadOnlyList<Comments> Comments => _comments.AsReadOnly();

    public void Discuss(Guid userId, string content)
    {
        if(Status != ProposalStatus.Pending)
            throw new DomainException("Can't discuss about an closed proposal");

        _comments.Add(new Comment(Id, userId, content));
    }
}