How to store a tree in a database?

Question

MySQL

I'm trying to figure out how to organize the storage of connections between crosses and couplings. Link is an optical cable that can link:

• cross-cross
  
• cross coupling
  
• coupling-coupling
  

In a simplified form, it looks something like this:

For me, the problem is that the connection can be either with a cross or with a clutch. Now I see the following implementation:

I would like to hear opinions on a more competent implementation of the database

Answer 1

objects
id | name | ident
1 | Муфта | mufta
...


links
id_object | id_child

In the objects table, we store the types of objects
. In the links table, links.
You can complicate things by adding such an entity to links as "scheme" or some sort of group specifier.
Variations can be made for a specific case

Answer 2

Is there a one-to-one relationship between the `cables` and `communications` tables? Then it is better to combine them into one table.
And it is not clear, in your system, the cable can still connect the cross with the cross or is it always only the cross with a clutch?