I think so but I do believe that it is more individualized than not. Head of institutions can be secretly holding but it is a bit complicated when two people or a group of people would decide on holding bitcoin. Certain emotions and judgment can be different for each individual and hence it is more accurate to say they are holding individually.
Why not it is possible if they make partnership and invest money by collecting together but it needs high level of trust as it is unable to access in more than one phone or PC, so in this case I think trust issue will come across otherwise it think it in this well developed age nobody needs to use it secretly but many are using openly.