Увеличьте порог, используя прогнозируйте вероятность
from sklearn.tree import DecisionTreeClassifier
clf = DecisionTreeClassifier(random_state = 2)
clf.fit(X_train,y_train)
# y_pred = clf.predict(X_test) # default threshold is 0.5
y_pred = (clf.predict_proba(X_test)[:,1] >= 0.3).astype(bool) # set threshold as 0.3
Weary Wombat