Replace ID column in LTREE with different column Postgres - postgresql

Question

I have a hierarchical structure in postgres which uses LTREE to calculate path based on a trigger. I am following the examples from here: https://coderwall.com/p/whf3-a/hierarchical-data-in-postgres
Table, trigger and data being inserted look like this:
CREATE TABLE section (
id INTEGER PRIMARY KEY,
asset_name TEXT,
parent_id INTEGER REFERENCES section,
parent_path LTREE
);
CREATE INDEX section_parent_path_idx ON section USING GIST (parent_path);
CREATE INDEX section_parent_id_idx ON section (parent_id);
CREATE OR REPLACE FUNCTION update_section_parent_path() RETURNS TRIGGER AS $$
DECLARE
path ltree;
BEGIN
IF NEW.parent_id IS NULL THEN
NEW.parent_path = '6'::ltree;
ELSEIF TG_OP = 'INSERT' OR OLD.parent_id IS NULL OR OLD.parent_id != NEW.parent_id THEN
SELECT parent_path || id::text FROM section WHERE id = NEW.parent_id INTO path;
IF path IS NULL THEN
RAISE EXCEPTION 'Invalid parent_id %', NEW.parent_id;
END IF;
NEW.parent_path = path;
END IF;
ltree_array = (STRING_TO_ARRAY(path::TEXT,'.'))[2:2147483647];
IF ltree_array IS NOT NULL THEN
FOREACH entry IN ARRAY(ltree_array)
LOOP
v_asset_name = (SELECT asset_name
FROM section AS s
WHERE s.id = entry);
s3path = s3path || v_asset_name || '/';
END LOOP;
END IF;
s3path = NEW.asset_store_id || '/' || s3path || NEW.asset_name;
NEW.s3_path = s3path;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER parent_path_tgr
BEFORE INSERT OR UPDATE ON section
FOR EACH ROW EXECUTE PROCEDURE update_section_parent_path();
INSERT INTO section (id, asset_name, parent_id ) VALUES (1, 'Main Folder', NULL);
INSERT INTO section (id, asset_name, parent_id ) VALUES (2, 'Rejected', 1);
INSERT INTO section (id, asset_name, parent_id ) VALUES (3, 'Records', NULL);
INSERT INTO section (id, asset_name, parent_id ) VALUES (4, 'Expired', 3);
INSERT INTO section (id, asset_name, parent_id ) VALUES (5, 'Selected', 3);
INSERT INTO section (id, asset_name, parent_id ) VALUES (6, 'Useless', 5);
The table output looks like this:
id|asset_name |parent_id|parent_path|
--|-----------|---------|-----------|
1|Main Folder| |6 |
2|Rejected | 1|6.1 |
3|Records | |6 |
4|Expired | 3|6.3 |
5|Selected | 3|6.3 |
6|Useless | 5|6.3.5 |
parent_path is all numerical because it looks like it is concatinating id, but I want to concatinate asset_name column.
I have tried replacing id with asset_name but that throws an syntax error. I can't seem to figure out how to replace id within the trigger.