Welcome Akshay, 
Please take time to review How to get help on the Dynamo forums
I had quite a few ideas how you could work out if cable trays are above each other, you could get the geometry min point, scale that in the z direction and check for intersection. I think this will work best as it localises the intersection to just above the geometry. Watch out for vertical cable trays.
Alternatively you could use linear algebra - a bit more complex but doable, however this is not localised as the object z plane will find any other aligned element (other levels, not overlapping etc.). Iām not 100% certain on my overlapping test either
