Carene is a natural product that is extracted from the resin of certain type of pine trees. It has the indicated structure. Please, use the "molecular panel" to have a 3D model.
 
It can be easily seen that one of the methyl groups severely hinders one of the two faces of the in-green olefin.
 

The face of the olefin at the opposite side to the cylopropane ring can easily reach the catalyst surface without any notable hindrance. Hence, hydrogenation takes place much faster by this face, leading to cis-carane,  which is the least stable of the two possible isomers. Trans-carane cannot be produced even though it is the most stable because it lacks the signaled steric interacton beteen the methyl groups. The approach of carene to the catalyst to render trans-carane is heavily hindered by one of the two methyl groups attached to cyclopropane ring.

The qualitative diagram of reaction energy should be similar to the following: 

  Pathway A bears a reasonable activation energy because the approach of carene to the catalyst surface takes place by its least hindered olefin face. Yet, this pathway produces the least stable cis-carane. There is a kinetic control of the reaction. The reaction is controlled by the way the olefin approaches the catalyst and not by the relative stability of the products. Besides, the mode of approach biases the stereochemical outcome of the reaction.
Pathway B has a much larger activation energy and proceeds at a much slower pace, even though it produces the most stable trans-isomer.  

The cyclopropane ring fused with the ciclohexene carries two stereogenic centers of fixed configuration. This fact makes the two faces of the double C=C bond have very different surroundings. The difference is so large in the case of carene and the molecule is so rigid that the hydrogen only adds to one of the two faces giving rise to a total facial selectivity.