MultiSelectListbox is used to select an item from a collection of listboxes that are in parent-child relationship.
<div class="card">
    <p:multiSelectListbox value="#{multiSelectView.selection}" effect="slide" header="Categories"
                            showHeaders="true">
        <f:selectItems value="#{multiSelectView.categories}"/>
    </p:multiSelectListbox>
</div>
package org.primefaces.showcase.view.input;
import jakarta.annotation.PostConstruct;
import jakarta.enterprise.context.RequestScoped;
import jakarta.faces.model.SelectItem;
import jakarta.faces.model.SelectItemGroup;
import jakarta.inject.Named;
import java.util.ArrayList;
import java.util.List;
import io.quarkus.runtime.annotations.RegisterForReflection;
@Named
@RequestScoped
@RegisterForReflection(serialization = true)
public class MultiSelectView {
    private List<SelectItem> categories;
    private String selection;
    @PostConstruct
    public void init() {
        categories = new ArrayList<>();
        SelectItemGroup group1 = new SelectItemGroup("Group 1");
        SelectItemGroup group2 = new SelectItemGroup("Group 2");
        SelectItemGroup group3 = new SelectItemGroup("Group 3");
        SelectItemGroup group4 = new SelectItemGroup("Group 4");
        SelectItemGroup group11 = new SelectItemGroup("Group 1.1");
        SelectItemGroup group12 = new SelectItemGroup("Group 1.2");
        SelectItemGroup group21 = new SelectItemGroup("Group 2.1");
        SelectItem option31 = new SelectItem("Option 3.1", "Option 3.1");
        SelectItem option32 = new SelectItem("Option 3.2", "Option 3.2");
        SelectItem option33 = new SelectItem("Option 3.3", "Option 3.3");
        SelectItem option34 = new SelectItem("Option 3.4", "Option 3.4");
        SelectItem option41 = new SelectItem("Option 4.1", "Option 4.1");
        SelectItem option111 = new SelectItem("Option 1.1.1");
        SelectItem option112 = new SelectItem("Option 1.1.2");
        group11.setSelectItems(option111, option112);
        SelectItem option121 = new SelectItem("Option 1.2.1", "Option 1.2.1");
        SelectItem option122 = new SelectItem("Option 1.2.2", "Option 1.2.2");
        SelectItem option123 = new SelectItem("Option 1.2.3", "Option 1.2.3");
        group12.setSelectItems(option121, option122, option123);
        SelectItem option211 = new SelectItem("Option 2.1.1", "Option 2.1.1");
        group21.setSelectItems(option211);
        group1.setSelectItems(group11, group12);
        group2.setSelectItems(group21);
        group3.setSelectItems(option31, option32, option33, option34);
        group4.setSelectItems(option41);
        categories.add(group1);
        categories.add(group2);
        categories.add(group3);
        categories.add(group4);
    }
    public List<SelectItem> getCategories() {
        return categories;
    }
    public String getSelection() {
        return selection;
    }
    public void setSelection(String selection) {
        this.selection = selection;
    }
}