Pour the chocolate chips into a glass bowl. Microwave them in 30 second intervals, stirring in between each interval until the chocolate is completely melted and smooth.
Line a cookie sheet or jelly roll pan with wax paper and use a spatula to spread the melted chocolate into the shape of a rectangle on top of the wax paper. The dimensions of the rectangle will end up being about 8"X12" - you don't want to spread the chocolate too thin, but if it's too thick, it won't harden as well either.
Sprinkle the crushed pretzels evenly on top of the chocolate.
Dice the green apple and use a paper towel to dab the apple pieces to absorb any extra moisture.
Unwrap the caramels and place in a microwave-safe bowl. I like to add 2 tablespoons of water to help thin out the caramel just a little bit. Microwave the caramels for one minute and then stir the mixture. Continue to microwave the caramels in 30 second intervals, stirring in between each interval until completely melted and smooth.
Add the diced apples to the caramel and mix until well combined. Spread the caramel/apple mixture on top of the pretzel layer. This layer is a little bit tricky to spread because it is so thick. This process is much easier if you spoon the mixture all over the pretzel layer so that each spoonful doesn't have to be spread very far.
Refrigerate for at least an hour before cutting into pieces. Refrigerate until ready to serve. You will want to serve and eat the bark within about 24 hours or the pretzels start to get soggy.