// 1) Create an action node component and (optional) add this attribute.
[GenerateAuthoringComponent]
public struct SeekEnemy : IComponentData { }

public sealed class BTSeekEnemySystem : SystemBase
{
   protected override void OnUpdate()
   {
       var beginSimECB = this.CreateBeginSimECB();
       
       Entities
           .WithAll<SeekEnemy>() // 2) Simply add it to your Query.
           .ForEach((Entity agentEntity, 
           // The parameters below are just up to you. 
           in EnemyLink enemyLink, 
           in LocalToWorld ltw,
           in StoppingDistance stoppingDistance, 
           in BTActionNodeLink bTNodeLink) => // 3) But don't forget to add this component in the end.
           {
               var position = GetComponent<LocalToWorld>(enemyLink.Value).Position;

               if (math.length((position - ltw.Position)) < stoppingDistance.Value)
               {
                   // 4) When you decided that the action was completed successfully, then you need to send the result.
                   beginSimECB.AddComponent(bTNodeLink.Value, BTResult.Success); 
               }
               else
                   beginSimECB.AddComponent(agentEntity, new MoveToDestinationRequest() { Position = position, Speed = 1f });
           })
           .ScheduleParallel();
   }
}

// 1) NOTE: in this case we need to implement interface IConditional. (It's only for conversion/validation purposes, not for runtime)
[GenerateAuthoringComponent]
public struct BTIsEnemyReachable : IComponentData, IConditional{ }

public sealed class BTIsEnemyReachableSystem : SystemBase
{
    protected override void OnUpdate()
    {
        var beginSimECB = this.CreateBeginSimECB();

        Entities
            .WithAll<BTIsEnemyReachable>()
            .ForEach(
            (DynamicBuffer<InteractableElement> interactableElements, 
            in EnemyLink enemyLink,
            in Name name,
            // 2) NOTE: we need to pass a Conditional Node reference.
            in BTConditionalNodeLink bTNodeLink) =>
            {
                for (int i = 0; i < interactableElements.Length; i++)
                {
                    if (interactableElements[i].value == enemyLink.Value)
                    {
                        beginSimECB.AddComponent(bTNodeLink.Value, BTResult.Success);
                        return;
                    }
                }
                // you also able to send "Fail" results.
                beginSimECB.AddComponent(bTNodeLink.Value, BTResult.Fail);
            })
            .WithoutBurst()
            .Run();
    }
}