I am trying to access a variable sent through a submit form. However it does not appear to be present once the form is submitted.

*see the hidden field on line: 2*

```
<%= form_for @import, html: { multipart: true } do |f| %>
  <%= f.hidden_field :tree_id, :value => @tree.id %>
  <%= f.label :new_branch_data %>
  <div class="help-text">Locate a file for import. (.xls, .xlsx file type)</div>
  <%= f.file_field :attachment %>
  <%= f.submit "Import", class: "btn btn-primary" %>
<% end %>

```

After hitting submit the action called in my controller:

```
def index
 @tree = Tree.find(params[:tree_id]) 
 ...
 ...
end

```

Hangs up on `@tree = Tree.find(params[:tree_id])` and returns a 

*"ActiveRecord::RecordNotFound" 
at /imports
Couldn't find Tree without an ID*

How can I correct this so that the @tree variable referenced in the form can be passed to the controller?