How to set tree loading time?

Question

I am working with TreeView in OpenERP. But my tree view takes a long time to load. How to set it up?

I defined the field Many2manyin the model product.product.

product_ids = fields.Many2many(
    comodel_name='product.product', 
    relation='product_procurement_rel',
    column1='process_id',
    column2='product_id',
    string='Products'
)

How can i solve this?