pile

疊 is composed of 畾(pile) and the variant of 宜(suitable). 畾 is the pictograph of three wheels stacked together, already conveying the idea of piling or accumulation, while 宜 means suitable or appropriate. Objects must be of suitable size and shape to be stacked layer upon layer without collapsing; thus 疊 expresses the meaning of stacking, piling up, or overlapping.