You're missing many connections (each element should be connected to one that's greater and minimal among the greater elements). You're also forgetting about $0$.
At the lowest level you have to place the minimum, that is, $1$.
At the next level, the primes: $2$, $3$, $5$, $7$, $11$, $13$, $17$ and $19$.
Next level, the products of two (not necessarily distinct) primes, that is, $4$, $6$, $9$, $10$, $14$, $15$.
Next level, the products of three primes: $8$, $12$, $18$, $20$.
Last level, the maximum, that is, $0$.
Connections:
- $1$ is connected to every term at the next level (the primes);
- $2$ is connected to $4$, $6$, $10$;
- $3$ is connected to $6$, $9$, $15$;
- $5$ is connected to $10$, $15$, $20$;
- $7$ is connected to $14$;
- $11$, $13$, $17$, $19$ are connected to $0$;
- $4$ is connected to $8$, $12$, $20$;
- $6$ is connected to $12$, $18$;
- $10$ is connected to $20$;
- $8$, $12$, $18$, $20$ are connected to $0$.