How can I improve the accuracy of my model? (Cab Cancellation Prediction)
Create addition variable: Eg: lead_time-start_time can be time to book.
Reduce variables with many classes if present (part of EDA)
standardize numeric variables - (val-mean)/sigma
Tree is a very weak classifier, you will have to do bagging or boosting (like ada boost or gbm or random forest
try parameter tuning - I am not pasting any links since I don;t know the policy for advertising over here, but just search GBM parameter tuning in google - you'll get multiple links

You have mentioned time issues when you tried ensemble methods. To solve that:

take a subset of data and try ensembling on that (once you finalize the model, run it on whole dataset)
if you are using XGBoost, you have an option of taking in another model as an input (you can run this in batches)