If we have purchased the land and this land having some trees which was the property of the first land owner. So how we claim for the trees

What country, what state?

Plantings are considered permanent additions to the property and stay with the land.

ANY question on law needs to include your general locale as laws vary by area. Its possible local laws may reverse that but I doubt it.

If we have purchased the land and this land having some trees which was the property of the first land owner. so how we claim for the trees

You own the land; therefore you own the trees. Is someone else asserting the right to cut the trees? Ask that person to show you something in writing.