Question: ![enter image description here](https://i.stack.imgur.com/PI2Q5.jpg)
Plant :Alstonia
Appearance:Blisters (gall) on both sides,cutting galls leaves white fluid.
After some time holes apppears in the blisters.so it seems some insect laid eggs.
What kind of disease is this? It seems to be some kind of blisters on the leaves of a decorative plant.
I'm guessing some insect laid eggs in it for eggs nourishment.

Would you please identify them and tell me how to treat them?

Answer: 
Alstonia scholaris (L.) R. Br. is a very beautiful ornamental tree, which is commonly known as pagoda tree because of its pagoda like growing habit. It is commonly infected by the Homopteran, Pauropsylla tuberculata Crawf which leads to unsightly gall formation on the leaves as pictured.
 The gall is the leaf response to the infection by the parasite which in turn sustains the growing insect. If there is a hole in the gall, the insect has likely already left. 

<https://www.cabdirect.org/cabdirect/abstract/20083091676>
I agree, leaf galls. Looks like a Rhododendron regardless, @Atul, need you to take a razor blade and slice through a 'gall' to see if the insect is still there. Take a picture. I would right now cut that infected branch off. This is usually not a death sentence! But before 'trying' any treatment we need to know what that insect is...or virus or bacteria but I am guessing insect. Later, Atul, lets talk about soil improvement. Plants that are stressed by poor environmental conditions are far more susceptible to insect or disease damage. Gaggy soil.

[leaf galls](https://www.google.com/imgres?imgurl=http%3A%2F%2Fcached.imagescaler.hbpl.co.uk%2Fresize%2FscaleWidth%2F620%2Fofflinehbpl.hbpl.co.uk%2Fnews%2FWOH%2F23_GallMiteDamageJuglansDoveAss_rt-2014052812345637.gif&imgrefurl=http%3A%2F%2Falfa-img.com%2Fshow%2Fpetunia-pests-and-diseases.html&docid=P8KDOQSHa9_SoM&tbnid=ylcP9Q2NYaeoiM%3A&vet=1&w=500&h=333&bih=735&biw=1455&q=rhododendron%20leaf%20gall&ved=0ahUKEwjIgtPtsKfRAhUC62MKHbs7ATAQMwgaKAAwAA&iact=mrc&uact=8) - [leaf gall](https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwi_0JX8s6fRAhVH5mMKHcv4BocQjRwIBw&url=https%3A%2F%2Fentomologytoday.org%2F2015%2F06%2F11%2Fgalls-insects-behind-the-weird-growths-on-plants%2F&bvm=bv.142059868,d.cGc&psig=AFQjCNEx9BzQ8XVmHHJJEzogJlDcSmEJig&ust=1483582004236157)