Although Real Madrid won the game but I find a very late and single goal insufficient for a team like Real Madrid facing a team like Union Berlin which isn't that top this season which make things worse. Real Madrid need to be convincing and score more goals. I wonder know what they could do if Bellingham was injured or carded..
Oh, I'll continue your thought further 
What would the Real Madrid players have done if the ball hadn't successfully bounced to Bellingham at the end of the match? I really feel sorry for the Union Berlin players that they could not endure a little bit until the final whistle of the referee and get a draw and one point in the standings. Despite all the advantage of Real Madrid in the second half, the Berliners defended the whole match with dignity. And yes, I will not call Union Berlin the strongest team, and if Real Madrid wants to achieve something this season in the Champions League, then the team needs to urgently strengthen the game when it really has to play with the strongest teams.