FlexReport provides the Legacy Chart field, and it uses the C1.Win.C1Chart and C1.Win.C1Chart3D assemblies to render chart fields consisting of 2D and 3D chart types, respectively.

In order to view the Chart  buttons in the Insert tab, select the check-boxes against Show "Legacy Chart" button on the INSERT tab from the FlexReportDesigner Options on the General tab.

For more information on 2DCharts and 3DCharts, see 2DChart documentation and 3DChart documentation, respectively.