Student Expense Tracker

College students often lose track of where their money goes each month — UPI payments, canteen bills, recharges, travel. There's no simple tool that works from the command line without needing an app or internet.

Your task: Build a Python command-line program where a student can:

1. Add an expense (date, amount, category — e.g. food, travel, recharge, other)
2. View all expenses they've added
3. See total amount spent
4. See which category has the highest spending

Bonus (optional): Add a feature to set a monthly budget and show a warning when spending crosses it.

Constraints: • Use only Python standard library + optionally pandas (no Django, Flask, or web frameworks) • No database needed — store in lists or dictionaries • Code should run without errors when we test it • Include at least 3 sample expenses already added so reviewers can see output immediately