In class we used decision trees and ensemble methods for classification, but we can use them for regression as well $($i$.$e$.$ learning a function from features to real values$).$ Let's imagine that our data has $3$ binary features A$,$ B$,$ C$,$ which take values $0/1,$ and we want to learn a function which counts the number of features which have value $1.$ Draw the decision tree which represents this function. How many leaf nodes does it have?