How to Design application database that have many accounts and each account have many users

I'm trying to design application with a database that has many company accounts and each account has many users one of them is account admin it looks like this tree

 Application Database
 |-> System Admin
 |-> System Users
 |-> System Users
 ___________________________________
 |                            |
 |-> Company 1 Account        |-> Company 2 Account          
        |-> Admin User        |-> Admin User
        |-> User              |-> User
        |-> User              |-> User
        |-> User              |-> User

each company accounts has some or all application model base on the company requirement

My question is How to design this application database without risking that the data from one company could be seen to other company or any data leaking I was trying to look for a similar design for this application database but I could not find