How to split two vertical pane inside a horizontal pane in tmux using tmuxinator

Currently am having this in my tmuxinator yml file,

windows:
   - editor:
       layout: main-horizontal 
       panes:
         - vim
         - 

  - server: rails s

This gives me 2 windows one for editor and another for server. In editor window i have two panes one for vim and another one is a blank pane where i can use some commands. But i want to split that blank pane further into two vertical pane i.e,

windows:
   - editor:
       layout: main-horizontal 
       panes:
         - vim
         - (I want to split this pane into two vertical pane, in which i can run my rails console in one pane and i can use the other for executing commands)

  - server: rails s

So totally i will have 3 panes in my first window. Could any one please help me in this.

Thanks.

If neither main-horizontal nor main-vertical is working for you. Then you can adjust your current layout the way you want to be and use the tmux cmd: list-windows witch will return the current layout. In Example:

list-windows returns:

1: bash [190x41] [layout c9f8,190x41,0,0[190x20,0,0,190x20,0,21{95x20,0,21,94x20 ,96,21}]]

Then the yaml will be:

windows:
   - editor:
       layout: c9f8,190x41,0,0[190x20,0,0,190x20,0,21{95x20,0,21,94x20,96,21}]
       panes:
         - vim
         - foo1
         - foo2
  - server: rails s