BinaryHeap constructor performs differently from heapify

I noticed that BinaryHeap like BinaryMinHeap constructs a heap that just insert every element from an array to a empty heap. And the following x and y have the same order:

julia> nums = rand(1:20000, 2000);

julia> x = MutableBinaryMinHeap(nums);

julia> y = BinaryMinHeap(Int.([]));

julia> for i in nums 
           push!(y, i)
       end

However, there is an O(N) heap-building algorithm instead of O(NlogN), and function heapify is an implement. So why not use heapify instead of insert successively？

Sincerely.