Check if all leaf nodes are at same level in ruby

Ruby program for Check if all leaf nodes are at same level. Here problem description and other solutions.

#  Ruby program for
#  Check if all leaves are at same level 

#  Binary Tree Node
class TreeNode 
	# Define the accessor and reader of class TreeNode
	attr_reader :data, :left, :right
	attr_accessor :data, :left, :right
	def initialize(data) 
		#  Set node value
		self.data = data
		self.left = nil
		self.right = nil
	end

end

class BinaryTree 
	# Define the accessor and reader of class BinaryTree
	attr_reader :root, :depth
	attr_accessor :root, :depth
	def initialize() 
		self.root = nil
		self.depth = -1
	end

	def checkLeafHeight(node, level) 
		if (node != nil) 
			#  Test node is leaf or not
			if (node.left == nil && node.right == nil) 
				if (self.depth == -1) 
					#  This is first leaf node
					#  Get node level
					self.depth = level
				elsif(self.depth != level) 
					#  When two leaf nodes is different level
					self.depth = -2
					return
				end

			end

			if (self.depth != -2) 
				#  Recursively visit left and right subtree
				self.checkLeafHeight(node.left, level + 1)
				self.checkLeafHeight(node.right, level + 1)
			end

		end

	end

	def isSameLevelLeaf() 
		self.depth = -1
		#  Test
		self.checkLeafHeight(self.root, 1)
		#  Display result
		if (self.depth < 0) 
			#  Two possible case
			#  1) When tree empty
			#  2) When leaf node are not same level
			print("No\n")
		else
 
			#  When leaf node is same level
			print("Yes\n")
		end

	end

end

def main() 
	#  Create new tree
	tree = BinaryTree.new()
	#    Make A Binary Tree
	#    --------------------
	#      1
	#     /  \
	#    2    3
	#   /    /  \
	#  4    5    6
	# insertion of binary Tree nodes
	tree.root = TreeNode.new(1)
	tree.root.left = TreeNode.new(2)
	tree.root.right = TreeNode.new(3)
	tree.root.right.right = TreeNode.new(6)
	tree.root.right.left = TreeNode.new(5)
	tree.root.left.left = TreeNode.new(4)
	tree.isSameLevelLeaf()
	#  Add new node
	tree.root.left.left.left = TreeNode.new(7)
	#   When add new node
	#    -----------------------
	#          1
	#         /  \
	#        2    3
	#       /    /  \
	#      4    5    6
	#     /
	#    7  
	tree.isSameLevelLeaf()
end

main()

Output

Yes
No