function drawVerticalBars(layersSelection) {
            let layerJoin = layersSelection
                .data(layers);

            layerElements = layerJoin
                .enter()
                .append('g')
                  .attr('transform', ({key}) => `translate(${xScale(key)},0)`)
                  .classed('layer', true);

            let barJoin = layerElements
                  .selectAll('.bar')
                  .data(({values}) => values);

            let bars = barJoin
                  .enter()
                    .append('rect')
                      .classed('bar', true)
                      .attr('x', (d) => xScale2(getGroup(d)))
                      .attr('y', ({value}) => yScale(value))
                      .attr('width', xScale2.bandwidth)
                      .attr('fill', (({group}) => categoryColorMap[group]));

            if (isAnimated) {
                bars.style('opacity', barOpacity)
                    .transition()
                    .delay((_, i) => animationDelays[i])
                    .duration(animationDuration)
                    .ease(ease)
                    .tween('attr.height', verticalBarsTween);
            } else {
                bars.attr('height', (d) => chartHeight - yScale(getValue(d)));
            }
        }
Draws the bars along the y axis
@param  {D3Selection} layersSelection Selection of layers
@return {void}