Pie charts often get a bad rap in data visualisation circles (sorry) but here is a technique to avoid those multiple small segments.
In the image below I have a sorted PivotTable of categories. I added the test1, test2 etc as examples of small value categories. We want to combine all the test categories into a separate segment.
Click in the PivotTable. In the PivotTable Analyse tab click the PivotTChart icon.
Select Pie on the left and then Pie of Pie on the right (third icon) – see below. Click OK.
Click the second pie chart.
Press Ctrl + 1 to open the Format Task Pane.
In the Series Options use the settings in the image below.
Feel free to adjust the settings as required.