With regards to the whole world casualties of Covid-19, the number most currently available is around 1.2M, or more precisely 1,202,081. If we were to interpret the statement in the most literal fashion imaginable, we'd have around 37.99 × 20M trees. Or to round it up, it'd be around 759.7 million trees. However, the Amazon Rainforest back in 2013 had an excess of 390 billion trees. While the amount of trees is significant, it's still only 1.9 per thousand in comparison to the Amazon back then.

However, such a point is moot since the deficit of humans relative to Covid-19 is easily covered with explosive population growth in regions like Africa.