将平铺的菜单数据(list)转换为树形(tree)结构

描述：在工作中，前端往往希望直接得到一颗树形结构数据做直展示，例如菜单、权限等，先记录一下主要编码

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1.构造数据

/**
 * 原始菜单数据
 */
public class Menu {

    private Long id;
    private Long parentId;
    private String name;
    private Integer sort;

    public Menu(Long id, Long parentId, String name, Integer sort) {
        this.id = id;
        this.parentId = parentId;
        this.name = name;
        this.sort = sort;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Long getParentId() {
        return parentId;
    }

    public void setParentId(Long parentId) {
        this.parentId = parentId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getSort() {
        return sort;