Preheat oven 350°F.Spray loaf pan with nonstick cooking spray Measure out ⅓ cup of chocolate chips and set aside. Pour remaining chocolate chips in a small microwave-safe bowl. Melt chocolate in the microwave starting with 1 minute. Stir and continue heating in 30-second intervals stirring in between a reheating until melted.Set aside to cool slightly while preparing the other ingredients. In a medium mixing bowl; combine flour, baking soda, and salt.
In a large bowl, beat butter and sugar with a whisk or a mixer until fluffy.Add eggs, maple syrup, milk, and mashed banana. Mix until completly combined. Stir the dry ingredients into the wet ingredients with a spatula just until combined (don't over mix).
Pour 1 cup of batter into the melted chocolate, stir until combined.
Pour ½ of the banana batter into the bottom of the prepared loaf pan followed by ½ of the chocolate batter. Pour the remaining banana batter then the remaining chocolate batter on top (using a spatula to smooth out the layers if needed). Using a butter knife, make a few swirls in the batter about 4 or 5 swirls (don't over mix).Top with reserved chocolate chips. Bake 70-75 minutes or until a toothpick comes out mostly clean (a couple of crumbs are fine).Let cool 10 minutes before transferring to a cooling rack to cool completely. Slice and serve. Store in plastic wrap, tin foil, or an airtight container for up to 4 days on the counter and up to a week in the refrigerator.