[指针] 求助一个关于指针的问题

MODULE typedef
    IMPLICIT NONE
    TYPE :: tree
        INTEGER,ALLOCATABLE :: mat(:)
        INTEGER :: a
        TYPE(tree),POINTER :: ltree
        TYPE(tree),POINTER :: rtree
    END TYPE
END MODULE typedef

PROGRAM test
    USE typedef
    IMPLICIT NONE
    TYPE(tree),POINTER :: root => NULL()
    TYPE(tree),POINTER :: temp1 => NULL(),temp2 => NULL()
    
    ALLOCATE(root,temp1,temp2)
    ALLOCATE(temp1%mat(5),temp2%mat(6))
    temp1%mat = 1
    temp2%mat = 2
    temp1%a = 1
    temp2%a = 2
    root%ltree => temp1
    root%rtree => temp2
END PROGRAM test