I have to write an essay on this: In The White Tiger, Balram’s father states that “my whole life I have been treated like a donkey. All I want...

Based on the quote you provided above, it can be argued personal freedom is necessary for a fulfilling life.

Ideally, the thesis statement should appear in the first paragraph. It should clearly describe your position and briefly explain why readers should care about your argument. If personal freedom is necessary for a fulfilling life, what does that life look like? That's an angle worth exploring. Essentially, to be free, one must have autonomy: the ability to decide one's course in life. 

Consider whether Balram has autonomy. Sure, he takes matters into his own hands, but does he have autonomy by the end of the story? Is the freedom he "purchases" through his murder of Mr. Ashok worth the risk of arrest? Or will Balram have to live the rest of his life looking over his shoulder and bribing the right people to preserve his freedom? In such a case, it can be argued Balram does not have the kind of freedom that allows him true autonomy. He may have acquired financial freedom and even freedom from a tyrannical master. However, he cannot live a life of authenticity; his present behavior is subject to his past immoral actions.

By killing Mr. Ashok, Balram achieves financial independence. However, he must live with the possibility that members of his family were murdered to avenge Mr. Ashok's death.

To get back to your thesis, here are some ideas (with suggested vocabulary):

While it is true that freedom is necessary for a fulfilling life, true freedom/independence/autonomy/self-determination cannot be secured by immoral actions.

Although Balram's murder of Mr. Ashok leads to his financial independence, his unprincipled/unethical/corrupt actions prevent him from achieving true freedom/independence/liberty/self-determination.

After deciding on your thesis statement, you can then use the body of your essay to expound upon your main idea. Refer to the text to discuss what unprincipled actions Balram resorts to in order to earn his financial freedom. Here are some ideas:

1) Balram kills Mr. Ashok and steals his money.

2) Balram leaves his family to deal with the consequences of his actions. From the text, we get the idea that he does not seem overly concerned about this. Balram seems to believe that the end justifies the means.

3) Balram has to bribe the police in order to maintain his new, privileged life in Bangalore.

Expand upon (1), (2), and (3) in separate paragraphs. In your last paragraph, explain why Balram does not really have true autonomy/freedom. While Balram rationalizes that all his actions have been worth the risk of getting caught, we get the idea that his newfound liberty is a precarious one. To protect his wealth and place in the "Light" of industrialized India, Balram must continue to resort to unprincipled/unethical actions. Based on such a shaky moral foundation, it can be argued that Balram's freedom is merely a facade.