This is what I keep advising others here to do. It is absolutely unsafe to store your entire coins on an exchange wallet which gives no access to that wallet's private keys. And even if they did, any kind of arrangement where you share access to your keys is a disaster and tragedy in the making. The safest way is for you and you alone to own, know and keep the private keys. Shared access is not compatible with sole and safe ownership.

Consider an analogy: joint bank accounts or supplementary credit cards. If the joint account holder or supplementary card holder spends the entire contents of that account or card, the main account or card holder absorbs the damage. Applying this to the exchange scenario, if they use your coins and refuse to reimburse you, there is almost nothing you can do, unless they operate in your country in which case there is a slim chance you might find recourse through the civil (and maybe even criminal) courts.

Trading can be nice and profitable, yes, but think and decide carefully when it comes to where to safely store those profits.