<apex:selectList value="{!selectedPicebookIds}" size="1">
                <apex:selectOptions value="{!PricebookNames}" />
                <apex:actionSupport event="onchange" reRender="bundle,allsections,errormesg" status="status" />
                <apex:actionstatus id="status">
                    <apex:facet name="start">
                        <div class="waitingSearchDiv" id="el_loading" style="background-color: #fbfbfb;
                               height: 100%;opacity:0.65;width:100%;">
                            <div class="waitingHolder" style="top: 74.2px; width: 91px;">
                                <img class="waitingImage" src="/img/loading.gif" title="Please Wait..." />
                                <span class="waitingDescription">Please Wait...</span>
                            </div>
                        </div>
                    </apex:facet>
                </apex:actionstatus>
            </apex:selectList>
            <br/>
            <br/> Bundle&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <apex:selectList value="{!selectedBundleId}" size="1" id="bundle">
                <apex:selectOptions value="{!BundleNames}" />
                <apex:actionSupport id="adOnProductType" event="onchange" status="status1" rerender="allsections,errormesg" /><!-- rerender="adOnInfo,errormesg,IncludedProInfo,product" /> -->
                <apex:actionstatus id="status1">
                    <apex:facet name="start">
                        <div class="waitingSearchDiv" id="el_loading" style="background-color: #fbfbfb;
                       height: 100%;opacity:0.65;width:100%;">
                            <div class="waitingHolder" style="top: 74.2px; width: 91px;">
                                <img class="waitingImage" src="/img/loading.gif" title="Please Wait..." />
                                <span class="waitingDescription">Please Wait...</span>
                            </div>
                        </div>
                    </apex:facet>
                </apex:actionstatus>
            </apex:selectList>

public List < SelectOption > getPricebookNames() {
            pricebookid = opp.Pricebook2Id;
            List < SelectOption > Options = new List < SelectOption > ();
            pricebookList = [select Id, name FROM Pricebook2 WHERE Id = : pricebookid];
            if (pricebookid != NULL) {
                for (Pricebook2 price: pricebookList) {
                    if (price.id == Opp.Pricebook2Id) {
                        Options.add(new SelectOption(Opp.Pricebook2Id, price.name));
                        getBundleNames();
                    }
                }
            } else {
                Options.add(new SelectOption('', '--Select--'));
                pricebookList1 = [select Id, name FROM Pricebook2];
                System.debug(pricebookList1);
                for (Pricebook2 price1: pricebookList1) {
                    Options.add(new SelectOption(price1.Id, price1.name));
                    getBundleNames();

                }
            }

            return Options;
        }
    public List < SelectOption > getBundleNames() {
        List < SelectOption > bundleOptions = new List < SelectOption > ();
        System.debug(pricebookid);
       if (pricebookid != NULL) {
            bundleList = [select Id, name, Price_Book__c FROM Bundle__c WHERE Price_Book__c = : pricebookid];
            System.debug(bundleList);
            bundleId = bundleList[0].Id;
            if (bundleList.size() > 0) {
                for (Bundle__c bundle: bundleList) {
                    bundleOptions.add(new SelectOption(bundle.Id, bundle.name));
                }
                BundlePopulatedRecordsMethod();
            } else {
                bundleOptions.add(new SelectOption('', '--Select--'));
            }
        }