How to display ltree in PostgreSQL nested set?

Question

PostgreSQL

Good afternoon.
There is a table with an ltree structure and it needs to be converted to a nested set.

StructureLtree(id INT PRIMARY KEY, value TEXT, path ltree);
    
    -- Данные:

    pk |  value  |  path  |
    0  |   'A'   |   ''   |
    0  |   'B'   |   '1'  |
    0  |   'C'   |   '2'  |
    0  |   'D'   |  '1.3' |
    0  |   'E'   |  '1.4' |
    0  |   'F'   |  '1.5' |
    0  |   'G'   |  '2.6' |
    0  |   'H'   |  '2.7' |

StructureSets(id INT PRIMARY KEY, value TEXT, lft INT, rgt INT);

, where the left and right borders of the node correspond to the rules for defining a nested set.
That is, the output will be something like

-- Данные:

    pk |  value  |  lft  |  rgt  |
    0  |   'A'   |   1   |   16  |
    1  |   'B'   |   2   |   9   |
    2  |   'C'   |   10  |   15  |
    3  |   'D'   |   3   |   4   |
    4  |   'E'   |   5   |   6   |
    5  |   'F'   |   7   |   8   |
    6  |   'G'   |   11  |   12  |
    7  |   'H'   |   13  |   14  |

Can anyone suggest an idea?

Answer 1

There is a cool guy on the Internet - Bill Karwin. He wrote about stacking different trees into relational tables.
And he also has a book "SQL Antipatterns. Avoiding the Pitfalls of Database Programming" there is also about trees.

Answer 2

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Answer 3

There are actually several options.
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