Bin size problem

I want to use TTree::Draw to get a spectrum and the data comes from an adc which has 4096 channels. If the bin size is just 1, I will get a smooth Guassian peak, however, everytiime when I use the function to draw the spectrum, the bin size is set by default to some large number, so I couldn’t get a smooth curve. What’s the default bin size? How can I change the default bin size when using the function?

Actually I am not so sure that I catch the key point because I doubt maybe there are other reasons. I attached a picture of a canvas. In the upper pad of the canvas, I use TTree::Draw to get a spectrum. I also created a histogram, and wrote same data into the histogram and displayed it in the lower pad. Why are they different?

Thank you very much!
c1.pdf (28.4 KB)

When you call TTree::Draw you can specify the number of bins and the limits for teh resulting histogram, eg


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