these are the most important organisation planting trees, see if there is one in your region, support or join them

Organisation Ecosia
Website https://www.ecosia.org/
Working in Latin America, Asia and Africa
Headoffice in Berlin Gemany
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Organisation One Tree Planted
Website https://onetreeplanted.org/
Working in North America, Latin America, Asia and Africa
Headoffice in Vermont USA
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Organisation Trees
Website http://trees.org/
Working in Africa
Headoffice in Silverspring USA
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Organisation The Fruit Tree Planting Foundation
Website http://www.ftpf.org/
Working in Across the world
Headoffice in Pittsburgh USA
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Organisation Urban Tree Alliance
Website http://www.urbantreealliance.org/
Working in North-America
Headoffice in Madison USA
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Organisation American Forests
Website https://www.americanforests.org/
Working in North-America
Headoffice in Washington DC USA
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Organisation Stand Earth
Website https://www.stand.earth/
Working in North-America
Headoffice in San Fransico USA
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Organisation Arbor Day Foundation
Website https://www.arborday.org/
Working in Mainly North-America
Headoffice in Nebraska USA
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Organisation Rainforest Action Network
Website https://www.ran.org/
Working in Across the world
Headoffice in San Fransico USA
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Organisation Rainforest Alliance
Website https://www.rainforest-alliance.org/
Working in Asia, Africa, North, Central and South America
Headoffice in Amsterdam The Netherlands
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Organisation The Center of People and Forests
Website https://www.recoftc.org/
Working in Asia
Headoffice in Bangkok Thailand
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Organisation Community Carbon Trees
Website http://www.communitycarbontrees.org/
Working in Costa Rica
Headoffice in San Jose Costa Rica
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Organisation Trees For All
Website https://www.treesforall.nl
Working in Bolivia, Oeganda and Nederland
Headoffice in Arnhem Nederland
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Organisation Nationaal Bossenfonds
Website http://www.nationaalbossenfonds.nl/plant-mee/
Working in Nederland
Headoffice in Arnhem Nederland
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Organisation Bos Plus
Website https://www.bosplus.be/nl/10miljoenbomen
Working in Blovia Ecuador Peru Vlaanderen
Headoffice in Gontrode Belgie
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Organisation Tree Nation
Website https://tree-nation.com/
Working in Colombia, Kenya, Nicaragua, Costa Rica, Madagascar
Headoffice in Barcelona Spain
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Organisation Trees For Life
Website https://www.treesforlife.org.au/
Working in Australia
Headoffice in Brooklyn Park Australia
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Organisation Carbon Neutral
Website https://carbonneutral.com.au/plant-a-tree/
Working in Western Australia
Headoffice in Perth Australia
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Organisation Tree Project
Website https://www.treeproject.org.au/
Working in Australia
Headoffice in Melbourne Australie
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Organisation Trees That Count
Website https://www.treesthatcount.co.nz/
Working in New Zealand
Headoffice in Wellington New Zealand
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Organisation Native Forest Restoration Trust
Website https://www.nfrt.org.nz
Working in New Zealand
Headoffice in Auckland New Zealand
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Organisation International Tree Foundation
Website http://internationaltreefoundation.org/
Working in Across the world
Headoffice in Oxford England
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Organisation Green Belt Movement
Website http://www.greenbeltmovement.org/
Working in Kenya
Headoffice in Nairobi Kenia
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Organisation Tree Aid
Website https://www.treeaid.org.uk/
Working in Africa
Headoffice in Bristol England
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Organisation Trees 4 Trees
Website https://trees4trees.org/
Working in Indonesia
Headoffice in Semarang Indonesia
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Organisation WeForest
Website https://www.weforest.org
Working in Brazil, India, Zambia, Tanzania, Ethiopie
Headoffice in Overijse Belgie
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Organisation SankalTaru
Website https://www.sankalptaru.org/
Working in India
Headoffice in Uttarakhand India
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Organisation Grow Trees
Website https://www.grow-trees.com/
Working in India
Headoffice in Mumbai India
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Organisation Say Trees
Website http://saytrees.org/
Working in India
Headoffice in Bangalore India
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Organisation PATT Foundation
Website http://www.pattfoundation.org/
Working in Thailand
Headoffice in London England
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Organisation Amazon Aid
Website https://amazonaid.org
Working in Brazil Peru
Headoffice in Charlottesville USA
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Organisation Tree Canada
Website https://treecanada.ca/
Working in Canada
Headoffice in Ottawa Canada
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Organisation World Wildlife Fund
Website https://www.worldwildlife.org/initiatives/forests
Working in World
Headoffice in Washington USA
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Organisation Eden Projects
Website https://edenprojects.org/
Working in Nepal, Madagascar, Haiti, Indonesia, Ehtiopia
Headoffice in Glandora USA
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Organisation Reforest The Tropics
Website https://reforestthetropics.org/
Working in Tropics
Headoffice in St Mystic USA
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Organisation Tree Sisters
Website https://www.treesisters.org
Working in Tropics
Headoffice in Bristol England