Tee is right angle flow valve as fluid enters one side and goes on the other side and has three opening similar to what  we buy Tee for plumbing from home depot. The name is same and function is almost the same but it is very high-pressure product pressure ranging from 2 k to 20 k psi. Flanges are connected to the 3 sides of the Tee.

 

Cross is same as Tee, except it  has 4 sided openings and it is used when there are two wings of production trees. All 4 sides have different connections or flanges to connect with Gate Valves or Choke Valves etc. Both tee and crosses are connected in the center of the production tree.