Visualize the Butterfly pattern with mirrored stars on both sides of each row, expanding toward the center then contracting.
A symmetric wing-like pattern. Each row has stars on both the left and right sides with empty space in the middle, widening toward the centre.
For each row, stars = row level, spaces = (2n-1) - 2*stars. The top half expands; the bottom half is the mirror image.
The butterfly has 2n-1 rows. The middle row (i=n) has no space: it is a full row of 2n-1 stars. The pattern is vertically symmetric around this row.