A Decision Trees developer designs and implements decision tree algorithms, which are used to solve classification and regression tasks in machine learning. They analyze large datasets, identify relevant features, and split the data based on these features to make predictions. They also handle tasks like pruning to avoid overfitting, choosing the best split point to improve accuracy, and visualizing the tree structure for better understanding. They work with other machine learning methods, and often use statistical techniques to improve model performance. Their goal is to create models that can make accurate decisions or predictions based on data.