Well, its uncertain if the price of Bitcoin will decrease further. Many speculated that it can happen so they're waiting for that before they buy to avoid losses but we cant really predict if it will going to happen or the price might recover consistently since anything is possible when it comes to Bitcoin's movement.
Anyway, the current price is still cheap if we're going to compare it for the past months, thus its fine to buy especially if you plan to hold for long term. Of course its risky because we dont know what could be the next movement right after you buy, but as long as you're not selling and willing to wait for the right time to take profit then you wont lose anything. Its only the price that turn downward but not the number of Bitcoin that you hold.
Even if you think that the price will no longer fall, you still should not buy for the entire available deposit. You need to take into account different outcomes, both the growth and the further fall of bitcoin, and it is for this case that you should have reserves so that you can buy at a lower price, and not just watch a further fall, without the ability to buy. Yes, in the future it will still grow, but also don’t want to miss the opportunity to buy more bitcoin.