The Bodhi Tree (Bo Tree) or the pipal tree is often mentioned as a Sacred Tree having significant associations with Buddha Gotama.
Prince Siddhattha finally arose fully Enlightened as Gotama Buddha under the shade of the Bodhi Tree which is said to have been “born” simultaneously with Him.
Thus the Bodhi Tree is the sanctified image of worship (pay respect) as a worthy Paribhogha Cetiya or shrine in Buddhist countries.
Buddhists therefore pay respect to the Bodhi Tree that has sacred association with the Buddha.
Source : Posted by Ye' Thu Aung (Buddhism for Beginners)