I have read a lot on how to prepare trees for shipping. The thing is how long can a bare rooted trees survive in the shipping? I am from Malaysia and would like to ship to UK. Please help

It depends how you cover the root ball in moist media and make the root ball airtight to avoid dessication; as well as depends on heat and other environment during transit.
Here is something that always encourages me. It is about a shipment sent to me inside Canada that took 57 days in transit (got stuck somewhere!) and survived to green up.
http://figs4funforum.websitetoolbox.com/post/fig-plants-resilience-for-survival-a-record-or-what-3718364

Thanks OttawanZ5 for the advice. I will be sending a guava tree and am wondering if it is ok to send during winter or do I have to wait until it's a bit warmer in the UK.

Better send in the winter. Your winters are mild.

not sure how cold UK is.. but i would worry about freezing and thawing also. i think repeated freezing and thawing can cause rot. 

Will the bubble wrap help to insulate the tree?

Have root ball surrounded by damp coco coir, then wrap in bubble wrap. Hope that the weather in the UK stays above 29 degrees.