The ornamental design for a tieredbuststraplessgown, as shown and described.
FIG. 1 is a top front perspective view of a tiered bust strapless gown with slit, showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The even broken lines shown in the drawings depict portions of the garment that form no part of the claimed design. The dot-dash broken lines shown in the drawing depict boundary lines and form no part of the claimed design.