I got the solution for my Question from AddToTree of org.apache.jmeter.gui.action package as guiPackage.getTreeModel().addComponent(testElement, parentNode);
Here, guiPackage is an instance of org.apache.jmeter.gui.GuiPackage class.
Testelement can be created using guiPackage.createTestElement(classname).
guiPackage.getCurrentNode() will provide currently selected node.
finally guiPackage.getTreeModel().addComponent(testElement, parentNode) will add the testelement as a child of parent node.
Thank u