Total no. of levels with 1024 elements is 11.Its better if you try drawing the heap.
For 512 to be at level 2 (on left subtree) the heap will be like, 0,512,1,513,514,2,3,515,516,517,518,4,5,6,7…
Since from 0 to 1023 there are 1024 elements so the heap will have just one element at the last level. We try to make this element as 512.
I take a small example. For 16 elements 0 to 15, I need to make 8 come at the last level. This is how I can do that: 0,1,2,3,4,5,6,7,9,10,11,12,13,14,15,8.
Similarly in the heap with 1024 elements, the 2nd last level will contain 512 elements (2^{9}) and those will be 511,513,514…1023 and at the last level, the left child of 511 will be 512.